Little Rock (US): A bus ferrying migrant farmworkers from Michigan to Texas ran off a highway and hit an overpass in Arkansas, ripping off the roof and ejecting passengers onto the interstate. Six people were killed and six injured; the driver survived.

The crash on Interstate 40 in North Little Rock happened yesterday at about 1 am, in light rain and fog following a heavy storm, but it wasn't immediately known whether weather played a role.

The National Transportation Safety Board investigation is initially focusing on the possibility of driver fatigue, though investigators may focus on other issues once they're on the scene, spokesman Eric Weiss said.

Roberto Vasquez, 28, was behind the wheel when the bus ran off the right side of the highway, struck a wall and hit the bridge. Vasquez told investigators his residence is in Arcadia, Florida, but his driver's license listed his address as Monroe, Michigan, Arkansas State Police spokesman Bill Sadler said.

Of those who died, three were thrown from the bus, one was partially ejected and the other two died inside, said Col Bill Bryant, the head of the Arkansas State Police.

Vasquez has agreed to routine drug and alcohol tests, but there's no indication he was intoxicated, state police Maj Mike Foster said.

The driver and two other employees of Vasquez Citrus and Hauling, a provider of foreign farm labour through the federal H-2A visa program, had been transporting 19 workers from Monroe, Michigan, to Laredo, Texas.

A woman who answered the phone yesterday at the Lake Placid, Florida-based company hung up as The Associated Press sought more information.

Twelve survivors of the crash are from Mexico, according to a list released late yesterday afternoon by Arkansas State Police. Three others live in Florida, while police didn't have a residence for another survivor. Their ages range from 19 to 43. The names of those killed are being withheld until all families have been notified, police said.