Washington, Aug 27, Harvey, which made landfall on Texas' Gulf coast as the most powerful storm to strike the US in 12 years, has left cities devastated and threatened to bring flooding with water as high as 1.3 metres.

Texas Governor Greg Abbott on Saturday said in the state capital Austin that authorities' primary concern was the "potential for very dramatic flooding", EFE News reported.

He said Harvey had already caused severe flooding in the coastal city of Corpus Christi, with half-metre-high water, and caused isolated flooding of up to 40 cm in Houston.

Abbott said nearly 300,000 people in Texas were without power and it could take days for electricity to be restored.

Harvey left one person dead in the coastal town of Rockport, Mayor Charles "CJ" Wax said on Saturday.

Officials said 12 to 14 persons in Rockport suffered minor injuries due to the hurricane, which made landfall with maximum sustained winds of 209 km (130 miles) per hour.

Residents witnessed widespread devastation, with streets converted into veritable rivers, trees uprooted, traffic signs knocked down, buildings destroyed and boats overturned.

Wax said Harvey, which has been downgraded to a tropical storm, had caused "widespread devastation", adding that some homes and businesses had been heavily damaged or completely destroyed.

The Miami-based National Hurricane Centre in its advisory said Harvey was "barely moving" and that torrential rains would continue.

The National Weather Service has advised Houston residents to avoid travelling. Three to four inches of rain was reported within an hour in the region.

Thousands of passengers on several Carnival cruise ships were stranded and unable to return to the Galveston in Texas.

The port of Galveston, where some Carnival cruise trips begin and end, was closed because of the storm.

Other Carnival cruises also changed plans with the port closed. The Carnival Freedom and Carnival Valor cruise ships remained at sea away from the storm, and each made a brief stop in New Orleans to replenish fuel, fresh water and food supplies, Carnival said in a statement.

The Bureau of Safety and Environmental Enforcement said about 25 per cent oil and gas production in the Gulf of Mexico had been halted due to the hurricane.

"It is also estimated that approximately 25.94 percent of the natural gas production of 3,220 million cubic feet per day, or 835 million cubic feet per day in the Gulf of Mexico has been shut-in," a BSEE report said.