powerful explosion hit a factory in eastern China’s Jiangsu Province Wednesday, killing a yet-unknown number of people and injuring many more, witnesses and hospital sources said.

An initial investigation showed gas leak triggered a blast at about 10:10 a.m. in a plastics factory at Mufu East Road, of Qixia District in northern Nanjing, capital of Jiangsu.

Xinhua reporters saw burnt corpses carried out from the site and buildings and vehicles within a 100-meter radius around the plant were seriously damaged.

The explosion hit a bus that was passing by the area, injuring many passengers.

Firefighters are trying to extinguish the blaze in the factory building.

Local residents said they felt a tremor and heard a loud noise, and many fled from buildings thinking it was an earthquake.

Authorities could not immediately give the number of casualties, but local media said more than 300 people have been hospitalized and at least 50 people were seriously injured