The blast occurred at about 10:10 am at an abandoned plastic and chemicals factory and an initial investigation showed gas leak from a pipeline going through the plant as the trigger of the explosion.
Authorities could not immediately give the number of casualties, but local media said more than 300 people have been hospitalised and at least 50 people were seriously injured.
Six people were confirmed dead at hospitals treating the injured people in Jiangsu province's capital Nanjing, sources reported.
Local residents said that they felt a tremor and heard a loud noise, and many fled out from buildings thinking it was an earthquake.
Buildings and vehicles within a 100-meter radius around the factory were seriously damaged. The impact of the explosion also damaged a bus that was passing the area, injuring many passengers.