At least 29 people died and four others were seriously injured when a bus went off a bridge in rural Thailand late Thursday night, a police official told CNN.

Investigators believe the driver may have been unfamiliar with the route and perhaps was going too fast, police Sub-Lieutenant Chatchawan Suwanput at the Lom Sak provincial police station said.

There were long skids marks where the bus went off the curving Huay Tong Bridge, he said.

The accident took place around 11.30 p.m. as the bus was on its way from Khon Kaen province to Chiang Rai province.

(Source: CNN)