CHENGDU, May 16 (Xinhua) -- A bus flipped over on Saturday, killing six people on board and injuring 20 others in southwest China's Sichuan Province, local authorities said.

The accident happened at 12:36 p.m. when the vehicle flipped over after crashing into the central guardrail on the highway from Xichang to Chengdu, according to the Sichuan provincial public security department.

Among the 36 people on board, two were killed on the spot and four died after being taken to hospital. All the 20 injured are treated in hospital, including three in severe conditions.

Further investigation of the accident is underway.