BEIJING — An explosion in Ningbo, a port city south of Shanghai, killed two people and injured at least 30 others Sunday, knocking down buildings and leaving streets littered with damaged cars and debris, the government said.

Firefighters traced the blast to a hole in the ground where a toilet had been but the cause was still under investigation, state television said online. It did not indicate if the explosion site was inside a building.

At least 30 people were taken to hospitals, according to Huanqiu.com, a site run by the Global Times newspaper.

The blast knocked down residential buildings, but they were vacant and being demolished, Huanqiu.com said.

Bystanders said the explosion might have been caused by a gas pipeline that was damaged, but the Ningbo gas company said it had no lines in the area, the China Youth Daily newspaper said online.

Video clips on multiple websites showed a cloud of smoke rising above the explosion site and rolling across nearby buildings. A photo on news.ifeng.com showed a room in an industrial building with a floor-to-ceiling hole in an exterior wall.

Associated Press