Rescue operations were ongoing after the fire broke out Tuesday in the Amur region that borders China, injuring more than 150 people at the isolated Amur Gas Chemical Complex (AGCC) -- a joint Russian-Chinese venture.

Russia's Amur GKhK, overseeing the site, said Wednesday it found the bodies of four more Chinese workers, a day after saying three people were killed.

"Thus, the deaths of seven people have been confirmed: one citizen of the Russian Federation and six Chinese citizens," the company said in a social media statement.

"The fate of nine other Chinese citizens, employees of a contracting company, remains unknown," it added.

It said 152 people sought medical attention, with 36 taken by a rescue plane to hospitals with wounds of varying degrees of severity.

The fire has been extinguished, the company said.

Amur Gas Chemical Complex (Amur GKhK) is jointly owned by Russia's Sibur and China's Petroleum & Chemical Corporation (Sinopec).

Accidents at Russian industrial sites -- including deadly ones -- are not uncommon.