Greyhound, the US-wide bus operator, cancelled all services across the United States today after a bus crashed, killing at least six people, when a passenger slit the driver's throat.

A passenger on the bus told a local television network that a man who looked to be in his early thirties had asked her for her seat then knifed the bus driver after she refused.

"He just went up to the bus driver and slit his throat and the driver turned the wheel and the bus tipped over," Carly Rinearson told WTVF from the crash site.

Six people were killed and the 32 others on board were injured, a spokesman for the Tennessee department of public safety said. The extent of the injuries was not immediately determined.

The bus was en route from Louisville to Atlanta when it crashed near the Tennessee town of Manchester, Greyhound said.

A spokeswoman said that the company had stopped all services as a precautionary measure after the crash. About 1,900 of the company's 2,300 buses had been on the road this morning, she said.

She said she could not confirm anything about the reported slashing.

The crash investigation has been turned over to the FBI.