Resorts on Padre Island, a popular holiday destination with many second homes, were subject to mandatory evacuation. The mayor of South Padre Island, Ed Cyganiewicz, said: "We may be criticised later for having everyone get off the island for no reason, but I'd rather err on the side of safety."
Some 3,000 inmates were taken in buses from jails in the area of Brownsville, close to the Mexico border.
If it maintains its current force, Bret will be the strongest hurricane to hit Texas since Beulah in 1967, which killed 13 people.
It has been more than 10 years since the area last experienced a severe hurricane, and local authorities fear that people are not taking the danger seriously enough. They did not start stockpiling staples and boarding up their homes until lunchtime on Saturday, resulting in long queues at DIY stores and supermarkets. One DIY chain shipped plywood from Houston to try to meet the demand. Emergency services said the greatest danger was likely to be flooding, and sandbags were being distributed to householders in vulnerable areas.
Galveston, south of Houston, was devastated by a hurricane in 1900, an event that lives on in folk memory and cost the city its pre-eminence as a port.