The most powerful hurricane to hit the US state of Texas in more than 50 years has killed at least one person and is now threatening catastrophic flooding as it lumbers inland and dumps torrential rains, according to US authorities.
One person died in a house fire in the town of Rockport, 48km north of the city of Corpus Christi, Mayor Charles Wax said in a news conference, marking the first confirmed fatality from the storm.
Harvey is the strongest storm to hit Texas, the center of the US oil and gas industry, since 1961.
The Mayor of Houston, Texas said Houston will receive two to three feet of rain in the coming days.
Sylvester Turner said: "This is serious ... It is important that people stay off the roads." He said that the city is prepared for what he described as a "major water event."
Earlier, US meteorologists said that Harvey has been downgraded to a tropical storm, but is lingering over Texas. They warned that it had unleashed "extremely serious flooding".
Harvey was not expected to move much for several days, meaning the state's Gulf Coast was going to see massive amounts of rain, the National Hurricane Center said.
Some communities could get up to more than 100 centimeters of rain.
"Rainfall of this magnitude will cause catastrophic and life-threatening flooding," the NHC said.
Earlier, Texas Governor Greg Abbott said he would activate 1,800 members of the military to help with the statewide clean-up while 1,000 people would conduct search-and-rescue operations.
The seaside town of Rockport, 48km north of the city of Corpus Christi, was hit hard.
Several homes had collapsed, and many more buildings suffered damage. Roofs had been ripped off some homes and windows were blown in.
The streets were flooded and strewn with power lines and debris. At a recreational vehicle sales lot, a dozen vehicles were flipped over and one had been blown into the middle of the street outside.
"It was terrible," resident Joel Valdez, 57, told Reuters. The storm ripped part of the roof from his trailer home at around 4am, he said. "I could feel the whole house move."
He 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.
Before the storm hit, Rockport's mayor told anyone staying behind to write their names on their arms for identification purposes 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.
The hurricane came ashore near Port Lavaca late yesterday with maximum winds of 209km/h.
That made it a Category 4 storm on the Saffir-Simpson scale, the second-highest category and the most powerful storm in over a decade to hit the mainland United States.
The streets of Corpus Christi, which has around 320,000 residents, were deserted early today, with billboards twisted and strong winds still blowing.
City authorities asked residents to reduce use of toilets and faucets because power outages left waste water plants unable to treat sewage.
Residents were also asked to boil water before consumption. The city was under voluntary evacuation ahead of the storm.
As many as 6 million people were believed to be in Harvey's path, as is the heart of America's oil-refining operations.
Thestorm's impact on refineries has already pushed up gasoline prices. The US Environmental Protection Agency eased rules on gasoline specifications late on Friday to reduce shortages.
US President Donald Trump, facing the first big natural disaster of his term, said on Twitter he signed a disaster proclamation that "unleashes the full force of government help" shortly before Harvey made landfall.
"You are doing a great job - the world is watching," he said in a tweet referring to the Federal Emergency Management Agency, which coordinates the response tomajor disasters.
You are doing a great job - the world is watching! Be safe. https://t.co/PJLdxy3hD9
— Donald J. Trump (@realDonaldTrump) August 26, 2017
Utilities American Electric Power Company Inc and CenterPoint Energy Inc reported a combined total of around 237,000 customers without power.
While thousands fled the expected devastating flooding and destruction, many residents stayed put in imperiled towns and stocked up on food, fuel and sandbags
