HONG KONG — At least six people have been killed and more are missing after a bus plunged into a sinkhole in the city of Xining, in northwestern China.

Video footage circulating on Chinese social media on Monday shows several people waiting to board the bus in Xining, the capital of Qinghai Province, when a traffic sign wobbles and the vehicle begins to sink into the road.

Bystanders rushed to help passengers escape from the sinkhole, which was at least 32 feet in diameter, according to Chinese state media, but they backed away as the bus slipped further into the widening hole.

Rescue crews worked overnight to free trapped passengers. Local business owners said they tried to help by breaking the bus windows to reach passengers.