A powerful explosion has hit a factory in eastern China's Jiangsu Province, killing a yet-unknown number of people and injuring more than 300.

An initial investigation showed a gas leak triggered the blast in a plastics factory. 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 say 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.