Houston  - With huge waves already rolling over Galveston Island and the Texas coast Friday morning, US President George W Bush sent an urgent appeal to stubborn residents who refused to evacuate.

Hurricane Ike was aimed dead-on to hit Galveston, a barrier island in the Gulf of Mexico, and Houston further inland, bearing winds of 195 kilometres an hour as it gathered steam over the warm Gulf of Mexico waters.

The storm is expected to make landfall between 0200 and 0600 GMT Saturday morning.

But with a reach of more than 400 kilometres from its center, Ike's winds have already pushed a storm surge and submerged more than half of the Galveston Island community of 60,000 by 1200 GMT Friday.

"Waters were nearing the tops of mailboxes and stop signs as darkening skies threatened rain. Water was streaming through the windows of ground-level homes," the Houston Chronicle reported online

Bush, speaking in Oklahoma, said he urged "fellow Texans to listen to what authorities are saying."

It was not known how many people had ignored mandatory evacuation orders, but police and firefighters made a final swoop through the town with a large dump truck to offer final escape to those who haven't evacuated.

Water levels could reach up to 7 metres in the course of the day, with waves pushing the level even higher, the National Hurricane Centre in Miami, Florida, predicted.

The National Weather Service has warned that "persons not heeding evacuation orders in single-family, one-or-two-storey homes will face certain death."

Fire Chief Pete David told the Chronicle he expected the storm to be the worst hurricane in memory for Galveston, which is known for its nearly 6-metre-high seawall built to protect historic old homes which survived the lethal storm of 1900.

In 1900, up to 8,000 people died after a huge hurricane hit Galveston, causing the deadliest natural disaster in US history. In 2005, Hurricane Katrina killed about 1,800 people in New Orleans and the surrounding Gulf coast.

The weather service predicted that average dwellings on the Galveston coast would be destroyed in large numbers, with "widespread and devastating personal property damage" even away from the shoreline.

Cars not driven out in the evacuation would "likely be swept away," while local roads could be washed away by hours of battering wave action while the hurricane passes over the island. The causeway that bridges to the island has been closed for incoming traffice except for media and rescue officials.

One person who chose to ride out the storm, Bobby Taylor, 47, told the Chronicle he knew it was "dangerous" but also "beautiful."

"The water doesn't frighten me," he was quoted as saying as waves rolled over his lawn.

Ike is a category 2 hurricane on the five-level Saffir-Simpson scale, but could reach the coast as a category 3 by the time it makes landfall, the hurricane centre said.

While waves posed the greatest threat, hurricane-force winds extend across a diameter of more than 360 kilometres.

Houston's skyscrapers were expected to lose windows, with roofs and trees in danger across the region.

In line with the extreme precautions taken in New Orleans last week, Houston mayor Bill White ordered an evacuation of 250,000 of the city's 4 million people.

Two weekends ago, nearly 2 million people evacuated from New Orleans and nearby Gulf Coast areas ahead of Hurricane Gustav. Less than a dozen deaths were reported from that storm. Many of the dead were the ill and elderly who died during the stress of evacuation. (dpa)