A disgruntled ex-worker shot dead one person and wounded five others in an office building in Florida on Friday before shouting "they left me to rot" as he was hauled into custody, police said.

In the second mass shooting in the United States in two days, the alleged shooter, 40-year-old Jason Rodriguez, apparently went to the office of his old firm and opened fire with a handgun, unleashing a hail of bullets on employees.

His eventual arrest at his mother's home after a tense, three-hour manhunt came as Americans reeled from a rampage 24 hours earlier at a Texas military base that left 13 people dead and 30 wounded.

Earlier, panicked Florida workers had barricaded themselves into their offices at the Gateway Center in central Orlando as SWAT teams combed through the 16-storey office building trying to find the shooter.

About three hours later, police acting on a tip converged on his mother's apartment where he surrendered without incident. It was not immediately clear if his mother or someone else had telephoned the authorities.

As he was dragged away by police in handcuffs he could be heard shouting to reporters in live television pictures, "They left me to rot," an apparent reference to his former employers.

"We have five that were victims of the shooting. We have one started having chest pains, and we do have one confirmed death," Orlando police chief Val Demings told a press conference.

"This is a tragedy, no doubt about it, especially on the heels of the tragedy in Fort Hood that is on our minds," Demings said. "I'm just glad we don't have any more fatalities or any more injuries than we currently have."

The Orlando shooting occurred as President Barack Obama ordered flags to be lowered to half-mast over Thursday's shooting at the Fort Hood military base in Texas in which 13 people were killed and 30 others wounded.

Given his outburst to journalists about being left to rot, Rodriguez is assumed to have been exacting revenge for his dismissal by architectural engineering firm Reynolds, Smith and Hills more than two years ago.

"He did work for us, for one year. He was let go in July 2007, he has been gone for over two years," Ken Jacobson, the chief financial officer of the firm, told AFP.

"We have not heard of or seen him since, that is what's hard to work out about all this," Jacobson said.

The Orlando Sentinel reported that Rodriguez underwent a state-ordered mental health evaluation the same month he was dismissed from the company, and filed for bankruptcy in September.

But a friend expressed his total shock that Rodriguez, a divorced father of an eight-year-old boy, was behind the shooting spree and described him as fundamentally a decent person who had been down on his luck.

"He couldn't find a job. He couldn't pay no bills. That's why he moved back with his mom," the friend, 46-year-old Ricky Falco, told AFP.

After being sacked by Reynolds, Smith and Hills, Rodriguez had been forced to take a job in a Subway sandwich bar but the pay had been too little to support him and he had quit a few months ago, Falco explained.

"When you can't find a job, and you've got bills to pay, wouldn't you be frustrated," he said. "They're making him look like a monster, and he's not. I know he killed somebody, but I think his brain just snapped."

Orlando offices and schools near the Gateway Center were earlier locked down as police SWAT teams conducted a frantic search for the killer with no obvious leads being reported for several hours.

A helicopter hovered overhead as workers fled the scene and dozens of police cars locked down the area surrounding the centre, dramatic television images showed.

"The gunman has been apprehended so the community is safe," Mayor Buddy Dyer told reporters after the drama ended.

"Obviously, we have had a tragic incident here in the city of Orlando, and first, our thoughts and prayers go out to the victims and the members of their family."

Mark Vella, 39, emerged from the 12th floor of the building where he and a half dozen colleagues barricaded themselves in their office using filing cabinets after seeing reports of what was going on downstairs on the news.

Vella, dressed in jeans and a T-shirt, said the group said prayers and planned how they would act if the gunman made his way to their office, until they heard Rodriguez had been apprehended.

"I said my prayers," he told reporters. "I'm glad it is over."