At least one dead, 250,000 without power as Hurricane Harvey smashes Texas

The most powerful storm to hit Texas in more than 50 years has killed at least one person, left 250,000 without power and is now threatening catastrophic flooding as it lumbers inland dumping torrential rains.

Hurricane Harvey hit the heart of the US oil and gas industry late Friday as a Category 4 hurricane with winds of 209km/h, making it the strongest storm to strike Texas since 1961.

The storm has ripped off rooves, snapped powerlines, and triggered tornadoes and flash floods. It has weakened to a tropical storm, but is expected to lash Texas for days, bringing as much as 102cm of rain.

The Category four hurricane smashed the heard of the US oil and gas industry. Source: AAP

One person died in a house fire in the town of Rockport as Harvey roared ashore overnight, Mayor Charles Wax said in a news conference on Saturday, marking the first confirmed fatality from the storm.

Earlier, Texas Governor Greg Abbott said he would activate 1,800 members of the National Guard to help with the statewide cleanup while 1,000 people would conduct search-and-rescue operations.

Billy and Donna Raney climb over the wreckage of whats left of their apartment after Hurricane Harvey destroyed it. Source: Getty

In Rockport, which took a direct hit from the storm, the streets were flooded and strewn with power lines and debris on Saturday. At a recreational vehicle sales lot, a dozen vehicles were flipped over and one had been blown into the middle of the street.

"It was terrible I could feel the whole house move," Joel Valdez said after the hurricane ripped part of the roof from his trailer home.

Valdez said he stayed through the storm to look after his animals.

"I have these miniature donkeys and I don't know where they are," he said, as he sat in a Jeep with windows smashed by the storm.

Resident Frank Cook, 56, also stayed through the storm.

"If you have something left of your house, you're lucky," he said, surveying the damage from his vehicle.

Before the storm hit, Rockport's mayor told anyone staying behind to write their names on their arms for identification in case of death or injury.

A high school, hotel, senior housing complex and other buildings suffered structural damage, according to emergency officials and local media. Some were being used as shelters.

The coastal city of Port Lavaca, farther north on the coast, had no power and some streets were flooded.

"There is so much tree damage and debris that the cost of cleanup will be enormous," Mayor Jack Whitlow told Reuters, after touring the city earlier Saturday.

One person died in a house fire in the town of Rockport as Harvey roared ashore overnight. Source: AAP

The streets of Corpus Christi, which has around 320,000 residents, were deserted on Saturday, with billboards twisted and strong winds still blowing.

City authorities asked residents to reduce use of toilets and faucets because power outages left wastewater plants unable to treat sewage.

A drill ship broke free of its mooring overnight and rammed into some tugs in the port of Corpus Christi, port executive Sean Strawbridge said. The crews on the tugs were safe, he added.

The city was under voluntary evacuation ahead of the storm.

Countless boats were sunk and sent flying onto roads around the state's coastline. Source: AAP

There are now fears major flooding will inundate areas of Texas. Source: AAP

Harvey was a Category 4 hurricane on the Saffir-Simpson scale when it hit the coast, the second-highest category, and the most powerful storm in over a decade to come ashore anywhere in the mainland United States.

Meanwhile US President Donald Trump, facing the first big natural disaster of his term, signed a disaster proclamation on Friday.

He met with his cabinet and staff on Saturday to discuss the federal reaction to the storm, according to a White House statement.

"President Trump emphasized his expectations that all departments and agencies stay fully engaged and positioned to support his number one priority of saving lives," according to the statement.