"Please stay where you are," said Gov. Rick Perry. "Be patient, stay put."
State officials said gridlock was starting again as people began to return to the densely populated Houston area, the fourth most-populated city in the United States.
"It appears that Houston and Galveston were spared the worst, but I want to re-emphasize to Texans in that area to remain in their homes, to remain in their places of safety," Perry told reporters.
State officials said they needed more time to replenish fuel supplies and restock food at grocery stores in the area.
They announced a plan to stagger the return of the evacuees over three days starting on Sunday, depending on the location of their homes. The state was providing evacuees with full details of the plan on the governor's Web site at http://www.governor.state.tx.us/.
"If you have gridlock, we can't get the fuel back in," said Texas Homeland Security Director Steve McCraw. "Even 1 million people will cause congestion."
When asked how Texas would enforce the return plan, McCraw said, "We're not going to pull people over and put handcuffs on them for not complying but quite frankly, Texans get it."
The highways leading out of Houston became clogged with 100-mile traffic jams on Thursday and Friday when initial projections of the powerful storm's path forced an evacuation from Houston and elsewhere along the Gulf of Mexico.
Traffic came to a halt as major roadways became parking lots and motorists ran out of gasoline, cars overheated and one bus caught fire, killing 24 elderly evacuees.
During the evacuation, the Texas Department of Transportation was criticized for being slow to open both inbound and outbound routes to speed the departure of more than 2.8 million people from the Houston and coastal areas.
With search-and-rescue crews coming to and from the area, Perry said it seemed unlikely state officials could turn the major roads leading to Houston into one-way traffic.
U.S. House of Representatives Republican leader Tom DeLay, who represents a Houston-area district, said it was not in evacuees' best interests to return immediately despite the natural urge to go back and check damage to their homes.
"The fact is that there is no gasoline in Houston at all," said DeLay, who drove from the city earlier in the day. "I know. I looked."