The explosion occurred early morning at a demolished factory in Jiangbei district of Ningbo City and also left two persons missing.
The site of the blast was without residents, but the nearby residential communities were affected, with some houses being damaged, local media reported.
Two people were killed and two others went missing in the explosion, State-run Xinhua news agency reported.
Fire fighters discovered a pot hole at the site, which is believed to be the source point of the explosion.
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The cause of the blast is still under investigation, the report said.
Two temporary relocation sites with quilts, food and medicine were arranged for the affected people, it added.
Earlier, reports said more than 30 people were taken to hospital, with two injured seriously, after the blast.
Ningbo is one of China's major international cargo and container shipping ports.
Scores of vehicles parked in the area were damaged.
Rescuers were seen trying to pull the people out of the rubble from flats whose roofs were blown off.
The restaurant owner, surname Feng, said his restaurant located near the explosion site suffered damage and glass windows broke when the explosion occurred.
He said the blast took place inside a roadside house that was used for commercial purposes and was due to be demolished soon.
China had a number of industrial accidents in the course of its massive economic growth.
Today's explosion resembled a series of explosions in 2015 in Tianjin port city which ripped through a warehouse, leaving 165 people dead, eight missing and 798 injured.
The majority of those killed were firefighting crews who had gone to douse the flames.
The blasts also damaged 304 buildings, 12,428 cars and 7,533 containers, incurring economic losses amounting to 6.87 billion yuan (USD 1.01 billion).