Heavy traffic and shortages of food and fuel are hampering the mass evacuation of a vast stretch of the US Gulf Coast.
More than one million people are trying to leave before Hurricane Rita, now a Category Four storm, makes landfall.
The storm, only slightly weakened, is heading towards Texas with winds over 150mph (240km/h) - stronger than the hurricane which devastated New Orleans.
The governor of Louisiana has urged people who live on the coast in the south-west of the state to head north.
Rita is set to reach land late on Friday or early on Saturday, and could be the most intense storm ever to hit Texas.
President George W Bush said the US was "preparing for the worst", adding that emergency procedures and personnel were ready.
Hurricane winds are radiating 70 miles (113km) from the eye of the storm - with the risk of heavy rains still posing a threat to New Orleans, where flood waters have only just been cleared.
Rita veered slightly north-east on Thursday, and New Orleans officials predicted up to 5in (12.7cm) of rain and a storm surge of up to 3ft (1m).
On the move
Many residents of Galveston and Corpus Christi, the two Texan towns feared to be in the path of the storm, seem to be heeding the calls to leave.
The BBC's Alastair Leithead in Galveston says authorities have been providing buses to get people out of town, as well as emergency supplies.
The southbound section of Interstate 45 into Houston was closed, and all eight lanes of the highway were dedicated to northbound traffic to help evacuees.
Nevertheless, roads and highways across the region were jammed solid on what was a hot Texas day.
Petrol stations are reporting shortages of fuel, and families are emptying supermarkets of non-perishable and long-life foods.
The acting director of the Federal Emergency Management Agency, David Paulson, called for patience, and said the long queues showed people were heeding calls for an early and comprehensive evacuation.
Moving fresh supplies of fuel into the region to help evacuees and rescue efforts was the agency's top priority, Mr Paulson said.
Weakened but savage
The eye of the storm was about 460 miles (740km) south-east of Galveston at 1500 GMT on Thursday, according to the US National Hurricane Center.
After strengthening to a Category Five, Rita weakened on Thursday but remains a "strong Category Four storm", the second highest on the Saffir-Simpson scale.
Moving at about 9mph (15km/h), it is forecast to make landfall in Texas as a Category Three storm, with winds of about 130mph (209k/ph).
"Everyone's scared, that's why we're all leaving," Galveston resident Maria Stephens told Reuters news agency.
"I saw the people at the shelters and the bodies floating in the water [after Hurricane Katrina]. I don't want that to be my family."
Several thousand Louisiana residents who found shelter in Texas after their homes were wrecked by Katrina are being uprooted again and moved to Arkansas and Tennessee.
More than 70% of oil production in the Gulf has been shut down, and US space agency Nasa has closed the Johnson Space Centre in Houston.
Federal authorities, criticised over their response to Katrina, have put emergency workers and medical teams on alert. Lorries filled with water, ice, food and medical supplies are on standby.
Precautionary measures have also been taken along the east coast of Mexico.
The confirmed number of deaths from Hurricane Katrina has reached 1,036, of which 799 were in Louisiana.