Hurricane Rita has weakened slightly but remains an extremely dangerous category-five storm taking aim at Texas.
President Bush said Thursday that authorities are "preparing for the worst" as the huge storm crosses the Gulf of Mexico with winds of 265 kilometers per hour.
In Texas, highways have been jammed with hundreds of thousands of motorists fleeing Galveston, Houston, and other cities in the storm's expected path.
Concern is growing that Rita will also affect neighboring Louisiana, which has just begun to recover from Hurricane Katrina.
Louisiana Governor Kathleen Blanco has urged residents to leave coastal areas, saying the state can expect "serious consequences" from the storm.
The U.S. National Hurricane Center now expects Rita to make landfall near Galveston late Friday or early Saturday.
On Wednesday, President Bush declared a state of emergency in Texas and Louisiana, and authorized the Federal Emergency Management Agency to coordinate disaster relief efforts.