San Francisco - A planned night out at the Casino turned into deadly mayhem when a bus packed with gamblers crashed on a rural California road Sunday night, killing eight passengers and injuring 35 more, police said Monday, lowering the original death estimate.

The driver of the bus, Quintin Watts, 52, was listed in critical condition. The California Highway Patrol said he was arrested for driving under the influence of drugs and that he had been involved in a crash two years and had a previous speeding conviction.

The CHP initially reported that 10 people had died in the crash but later amended that figure because some of the victims had been counted twice.

The crash occurred near the small town of Williams, about 180 kilometres north of San Francisco after the bus veered off the narrow road and then completely flipped over as it overcorrected.

Television pictures from the scene showed the mud-covered bus ended up back on its wheels, with its windows smashed and sides and roof mangled. Police said that some of the victims were thrown from the bus as it rolled over. Rescue officers spent hours searching through tall grass through the night trying to locate the victims.