A bus carrying elderly evacuees out of the path of Hurricane Rita has caught fire on a gridlocked motorway, killing 24 people, authorities say.
The bus was engulfed in flames, causing a 17-mile (27km) tailback on the Interstate 45 highway, the main route north from the Gulf Coast to Dallas.
Police spokesman Don Peritz said early indications were that the cause of the bus fire was mechanical.
The vehicle was reportedly carrying about 44 passengers.
Television pictures showed the entire bus alight, with explosions sending plumes of thick black smoke billowing into the sky.
Officer Peritz said there the blasts were apparently caused by oxygen containers for the elderly on board the vehicle.
The inferno reduced the bus to a charred shell, with just its frame remaining.
The passengers were being evacuated from a nursing home in Bellaire, south-west Houston, when the accident happened about 17 miles (27km) south-east of Dallas.
Care home management company Sunrise Senior Living said 28 residents and six employees from Bellaire's Brighton Gardens Assisted Living care home had been on the stricken bus.
In a statement, Sunrise chairman and chief executive Paul Klaasen said the company was "shocked and saddened that this event occurred during our evacuation".
Eyewitness Ashley Donald told Houston television station KTRK he saw the fire break out.
"It burst into flames with black smoke coming from the bus, and then we saw the fire," he said.
Officer Peritz said the driver, who survived the fire, repeatedly went back onto the bus to try to rescue passengers.
Dallas Mayor Laura Miller told CNN: "It's obviously a horrific event. The whole city is very upset about this. We've handled two waves of evacuees now. We've never had anything this horrible happen, so it's really a tragedy."
Lanes around the bus were closed off and traffic, already gridlocked, diverted from the scene of the accident near the town of Ennis.