Hurricane Rita strengthened into a powerful, intensely dangerous Category 5 storm today as it headed toward the Texas coast.
The US National Hurricane Centre said the storm had grown into the third most intense Atlantic hurricane on record as measured by internal pressure.
More than one million people along the Texas coast have already fled the approach of the Hurricane.
With winds of nearly 170 mph (273 kmh), the hurricane churned across the Gulf of Mexico on a course that was expected to take it ashore late tomorrow or early on Saturday.
Having learned a lesson from Hurricane Katrina's assault on Louisiana and Mississippi last month, city officials along the Texas coast told residents to clear out and arranged for buses for those who needed help.
Residents of the island city of Galveston, Corpus Christi and low-lying parts of Houston 50 miles inland were among the 1.3 million Texans told to evacuate.
People from Houston fleeing their city created bumper-to-bumper traffic jams on interstate highways that lasted well into the night.
New Orleans, still staggering after being flooded by Katrina, was taking no chances this time.
Mayor Ray Nagin said two busloads of people had been evacuated already and 500 other buses were ready.
Texas Govenor Rick Perry, who told people along a 300-mile (483 km) stretch of coast to leave, said computer projections were prepared for city officials so they could see what could be left underwater after being hit by Rita's storm surge.
"Between Katrina and our preparations for this, people understand this isn't something you're going to play around with," Mr Perry told CNN.
He said 5,000 Texas National Guard troops were on standby and 1,000 Department of Public Safety officers were along evacuation routes, ready to move in after Rita's landfall.
Shelters for 250,000 evacuees were being established in Huntsville, College Station, San Antonio and Dallas.
In Galveston, Mayor Lyda Ann Thomas said today up to 80 per cent of the vulnerable city's 60,000 residents had left.
"We'll have our police forces down there with the loudspeakers reminding people that they need to leave today - because tomorrow will be too late," she told CNN.
Corpus Christi Mayor Henry Garrett said the evacuation of his city was inspired by Katrina and was going smoothly.
By lunchtime today Rita's center was about 490 miles (788 km) southeast of Galveston and 595 miles (957 km) east-southeast of Corpus Christi with hurricane-force winds that extended 70 miles (110 km) from its center.
It was moving west-northwest at about 9 mph (15 kph), the US National Hurricane Center said.
Rita's maximum sustained winds of up to 175 mph (281 kph) over the warm waters of the Gulf matched the peak strength over water of Katrina, which hit land as a Category 4 storm with 145 mph (233 kph) winds.
The hurricane center expected Rita to weaken slowly but still make landfall as a major hurricane.