The Texan city of Houston will receive 2-3ft of additional rain in coming days, Mayor Sylvester Turner warned residents on Saturday as the most powerful storm to hit Texas in more than 50 years moved inland.
"This is serious," Mr Turner said in a televised interview as Hurricane Harvey turned into a tropical storm that was expected to linger over the mid-Texas coast. "It is important that people stay off the roads."
Mr Turner said the city, the fourth most populous in the US, is prepared for what he described as a “major water event”.
Houston has received about 16 inches (40cm) of rain as a result of Harvey, while neighbouring Corpus Christi has seen about 20 inches. Areas between the two cities could see another 20 to 30 inches of rain, Texas governor Greg Abbott said at a news conference in Austin, the state capital, earlier on Saturday.
The region is facing the prospect of catastrophic flooding from the torrential rains. Power outages have affected over a quarter million customers in the state and gas stations in Houston have been struggling to keep up with motorists’ demands.
Four refineries in South Texas have shut down, disrupting gasoline supplies and pushing prices higher. In addition, about 25 per cent of the US Gulf of Mexico’s oil production was offline as of midday on Saturday, according the US Bureau of Safety and Environmental Enforcement.
One person is reported to have died in a house fire during the storm.
Harvey has been measured as the strongest storm to hit Texas, the centre of the US oil and gas industry, since 1961.
The town of Rockport, 30 miles (48 km) north of the city of Corpus Christi, appeared to be one of the hardest hit. Ahead of the storm’s arrival, the city’s mayor had told anyone staying behind to write their names on their arms for identification purposes in case of death or injury.
"Right now we're still hunkered down and can't go anywhere," Steve Sims, the volunteer fire chief in Rockport, said early on Saturday.
“We’ve heard rumours of 1,000 different things, we can’t confirm anything because we haven’t seen anything. We know we’ve got a lot of problems, but we don’t know what yet.”
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.
Mr Sims said power, internet and most mobile phone services were cut in the town of 10,000, from which about two-thirds of the residents had evacuated. Most of the senior citizens’ and nursing homes were among the first to be evacuated, he said.
The hurricane came ashore northeast of the city of Corpus Christi late on Friday, and the maximum winds of 209km/h 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 about 320,000 residents, were deserted early on Saturday, where strong winds were still blowing.
Unable to treat sewage
City authorities asked residents to reduce use of toilets and taps on Saturday because power outages had left waste water plants unable to treat sewage.
The city also asked residents to boil water before consumption.
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.
US president Donald Trump, facing the first big natural disaster of his term, said on Twitter he signed a disaster proclamation which "unleashes the full force of government help" shortly before Harvey made landfall.
"You are doing a great job - the world is watching," Mr Trump said on Saturday in a tweet referring to the Federal Emergency Management Agency (FEMA), which co-ordinates the response to major disasters.
While thousands fled the expected devastating flooding and destruction, many residents stayed put in imperilled towns and stocked up on food, fuel and sandbags.
Harvey was the first major hurricane of Category 3 or more to hit the mainland United States since Hurricane Wilma struck Florida in 2005.
Its size and strength also dredged up memories of Katrina, the 2005 hurricane that made a direct hit on New Orleans as a Category 3 storm, causing levees and flood walls to fail in dozens of places. About 1,800 died in the disaster made worse by a slow government emergency response.