Investigators excluded the possibility of piped gas explosion in an accident that killed two people in east China's Zhejiang Province, local authorities said.

Two people died, 19 were injured including four with serious injuries, and two others went missing after an explosion at the site of a demolished factory around 8:50 a.m. on Sunday in Jiangbei district of Ningbo City.

Fire fighters discovered a pot hole at the site, which is believed to be the source point of the explosion. Local villagers said there was previously a toilet. It was confirmed to be a septic tank after investigation.

The site of the accident were without residents, but the nearby residential communities were affected, with some houses being damaged.

Two temporary relocation sites with quilts, food and medicines were arranged for the affected people.

The exact cause of the blast is still under investigation.