Houston  - Twelve hours after Hurricane Ike tore into Texas' Gulf Coast, rescue crews were trickling Saturday afternoon into the area around hard-hit Galveston, Texas officials said.

Rescuers immediately evacuated four patients from a University of Texas medical center in Galveston, the city on a barrier island where the storm pushed a surge of Gulf waters to a height of nearly 1 metre into the first floor of buildings, said Texas Governor Rick Perry in broadcast remarks.

Adjoining Galveston island, 125 people had been rescued from Bolivar Island, he said.

Perry said that Texas had organized and pre-positioned the largest rescue operation in state history, with five Blackhawk helicopters from the "Texas military," Coast Guard helicopters, air boats from the Texas park and wildlife agencies and special teams trained in fast-water rescue.

"As we speak, elements are reentering Galveston by air, by boat, by ground," he said.

He declined to offer an estimated death toll, because search-and- rescue efforts had just launched in Galveston, where more than 20,000 people elected to stay behind despite dire warnings and a mandatory evacuation.

Hundreds of emergency calls to the rescue centre on Galveston went unanswered early Saturday as firefighters and police were unable to move around in the
175-kilometer-an-hour winds.

CNN reported four deaths, including one of a 10-year-old boy killed by a tree that fell when his father was trying to clean up yard debris.

Federal Emergency Management Agency (FEMA) officials said that 1,000 rescue workers were already on the ground, "responding as quickly as we can."

"A lot of people did not evacuate, so it's going to take some time," FEMA chief David Paulison said.

A special task force onboard the USS Nassau in Virginia was steaming for the Gulf of Mexico with a surgical team and disaster relief crew on board.

"The first priority is life saving," Paulison said. "State helicopters, Coast Guard helicopters, Department of Defence helicopters, are out there trying to rescue people, particularly in Galveston, and the large number of people there who did not evacuate as they were told to."

US Homeland Security Secretary Michael Chertoff said: "This is still a dangerous storm. We want to minimize the loss of life as much as humanly possible."

Paulison warned that the worst accidents occur when people leave their homes too soon. "Everyone in the path of this storm needs to stay home," he said.

Tornadoes and dangerous lightning were forecast as Ike moved north-east through Texas as a weaker but still potent tropical storm.

Governor Perry said it seemed the Texas coast and its oil refining structures had dodged "the worst case scenario - particularly in the Houston ship channel."

The 64-kilometre channel connects Galveston to Houston and was the natural path for the 2.5 metre storm surge. Houston is home to 15 per cent of US petrochemical refining capacity, but the industrial sector was shut down and battened down ahead of Ike's arrival.

Petrol prices were beginning to rise at the pump while people waited in line to fuel their cars. (dpa)