Update 11.10am: Police have arrested the surviving Boston Marathon bombing suspect after a 22-hour manhunt and a widespread lockdown in the city.
The Boston Police Department made the announcement through Twitter today.
"Suspect in custody. Officers sweeping the area. Stand by for further info," the post said.
Boston police also tweeted: “CAPTURED!!! The hunt is over. The search is done. The terror is over. And justice has won. Suspect in custody.”
Dzhokhar Tsarnaev, 19, had been hiding in a boat in the backyard of the house, after being wounded in an overnight shootout in which his brother Tamerlan, believed to have been the second bombing suspect, was fatally shot.
Boston Police Commissioner Ed Davis said police, state troopers and FBI agents zeroed in on the boat on Franklin Street after a man went out of the house and saw blood on the boat.
The man then opened the tarp covering the boat and saw a man covered with blood inside, and called police.
“I’m so happy because the people in the greater Boston area will be able to sleep tonight because of the work of these individuals,” Boston Mayor Thomas Merino told reporters, in a tribute to police and law enforcement agencies.
The University of Massachusetts student was surrounded by a small army of police for a final showdown which lasted nearly two hours. Attempts to negotiate with him failed as he was “not communicating,” Davis said.
“Over the course of the next hour or so, we exchanged gunfire with the suspect who was inside the boat,” he said.
“And ultimately, the hostage rescue team of the FBI made an entry into the boat and removed the suspect who was still alive in the boat.”
Tsarnaev was taken from the scene in an ambulance and is in a serious condition. His injuries are not believed to be life-threatening.
At one stage, a series of about 15 explosions erupted, which local television channels said could have been stun grenades.
Boston residents, who had been told to stay home during the lockdown, cheered as police officers drove by upon confirmation the second suspect had been arrested.
In a statement after the suspect's capture, President Barack Obama pledged to "determine what happened".
“We will investigate any associations that these terrorists may have had. And we’ll continue to do whatever we have to do to keep our people safe,” he said.
In the Watertown neighbourhood where 19-year-old Dzhokhar Tsarnaev engaged in a firefight with police while hiding out in a parked boat, dozens of people at a police barricade cheered and applauded as law enforcement officers and emergency responders left the scene.
“Never in my wildest dreams did I think that this would result in a shootout in Watertown,” said Sheamus McGovern, who was among the crowd of people gathered outside Mount Auburn Hospital, where Tsarnaev was taken after his capture.
Hundreds of people later descended into the streets of Boston to celebrate, chanting: “USA! USA!“
The jubilation was widespread. The mayor of Boston, which was largely paralysed during the manhunt Friday, tweeted, “We got him!“ And at the home of the New York Mets, fans leapt to their feet and cheered when the news spread during a game against the Washington Nationals.
Hundreds of people marched down Commonwealth Avenue, chanting USA and singing the Red Sox anthem Sweet Caroline as they headed toward Boston Common. Police blocked traffic along part of the street to allow for the impromptu parade.
The 22-hour manhunt intensified late last night as gunfire was heard, believed to be part of the exchange with the suspect in the boat.
Police squads and armored personnel carriers raced to the district and police helicopters buzzed overhead after the gunfire.
The gunfire erupted in the district only minutes after police told a press conference they believed that Tsarnaev had escaped a mass dragnet thrown over Watertown.
The Boston Globe, CNN and other media on the scene all reported hearing numerous shots, and television images showed police cars swarming at high speed in the direction of the shots.
Boston Police Commissioner Ed Davis yesterday described the second suspect as “a terrorist” and warned he was "armed and dangerous" during the manhunt.
Authorities established a 20-block perimeter in the search for the suspect and police went door-to-door in their hunt for him. Residents were warned to stay indoors and “stay away from windows”.
Public transport in towns surrounding Boston was shutdown and stores in the areas were asked to remain closed.
The suspects were initially located after a police officer was killed and another wounded during a violent spree overnight that began at the Massachusetts Institute of Technology’s campus.
Davis said more than 200 rounds of gunfire were exchanged during that incident, and that the two men had hurled improvised explosive devices and handmade hand grenades at officers.
Heavily armed police swarmed through Boston streets after earlier responding to reports of gunfire at the Massachusetts Institute of Technology.
“There were blasts, it could have been grenades,” local resident Adam Brown said.
Boston Globe reporter Wesley Lowery tweeted that a “handcuffed male being questioned by FBI in back of ambulance”.
“Wasn't close enough to really see suspect. Was a male in white shirt. Not going to speculate his race,” Lowrey said in another tweet.
The university was in lockdown for nearly three hours until police were certain the gunman was no longer on the campus.
Witnesses said there were explosions and a carjacking.
Police with rifles are in the streets, and search helicopters flew above the university.
Students were told the situation was extremely dangerous while the gunman remained at large and to stay clear of the area or stay inside as police swarmed the campus.
Security guards and police had earlier surrounded a building.
After reports of gunfire, a statement on the MIT website said that "at 10:48pm today gunshots were reported near Building 32 (Stata) which is currently surrounded by responding agencies.
People were being urged to stay indoors and away from Building 32.
Cambridge police and the Middlesex District Attorney's office says the officer was responding to a report of a disturbance when he was shot multiple times.
The university also tweeted the warning to students and staff.
The 26-year-old elder brother died of bullet wounds and injuries from explosives strapped to his body, a hospital doctor said.
Police said the suspect that died had explosives on his body when he was captured and there were earlier fears the man on the run was armed with explosives as well as a rifle.
Authorities say the suspects threw explosives from a vehicle that had been carjacked as police followed it into Watertown.
The suspects and police exchanged gunfire, and one of the suspects was critically injured and later died in hospital while the other escaped.
Two suspects were said to be in police custody but police later confirmed that only one man was being held.
Local television showed vision of a man laying on the ground surrounded by armed police.
He later died at a hospital.
The university said it was “heartbroken by the news that an MIT Police officer was shot and killed in the line of duty“.
“Our thoughts are now with the family.”
Meanwhile, three people have also been taken into custody for questioning at a housing complex where the 19-year-old suspect may have lived.
New Bedford Police Lieutenant Robert Richard says a private complex of off-campus housing at the University of Massachusetts at Dartmouth was searched by federal authorities.
Richard says the FBI took two males and one female into custody for questioning.
He says Dzhokhar Tsarnaev may have lived at or was affiliated with the housing complex. He is registered at the school.
Yesterday, the FBI released images of the two suspects they wished to speak to in relation to bombings at the Boston Marathon.
One of the men was wearing a white cap and the other a black cap.
One of the suspects was seen carrying a backpack, which was placed at the scene of the second explosion.
US media reports the suspects are brothers from a Russian region near Chechnya, who have lived in the United States for at least a year.
NBC News reports men had “international ties” and “military experience”.
The dead suspect, Tamerlan Tsarnaev, was married with a child.
The suspects' father, Anzor Tsarnaev spoke to The Associated Press by telephone from the Russian city of Makhachkala today.
“My son is a true angel,” Mr Tsarnaev said.
“Dzhokhar is a second-year medical student in the US. He is such an intelligent boy. We expected him to come on holidays here.”
In May 2011, Dzhokhar, then a senior at a prestigious high school, was awarded a $US2,500 scholarship from the city of Cambridge, Massachusetts, to pursue higher education.
An uncle, Ruslan Tsarni, who lives in a Washington suburb, told The Associated Press that the men lived together near Boston and have been in the United States for about a decade.
They came from the Russian region near Chechnya, which has been plagued by an Islamic insurgency stemming from separatist wars.
Dzhokhar Tsarnaev’s page on the Russian social networking site Vkontakte says he attended Cambridge Rindge and Latin School, graduating in 2011, the year he won the scholarship, which was celebrated with a reception at City Hall, according to a news release issued at the time.
Dzhokhar Tsarnaev also posted messages on Twitter after the bombings telling people to "stay safe.
Before moving to the US, he attended School No. 1 in Makhachkala, the capital of Dagestan, a predominantly Muslim republic in Russia’s North Caucasus that has become an epicentre of the Islamic insurgency that spilled over from Chechnya.
On the site, he describes himself as speaking Chechen as well as English and Russian.
His world view is described as “Islam” and he says his personal goal is “career and money.”