The leak occurred when a valve on a storage tank belonging to Xingkesheng Chemical Co Ltd failed due to metal fatigue, authorities in the city of Chenzhou said.
Emergency treatment measures are being undertaken, including sealing the tank and erecting barriers on the Baoyuan River to intercept the leak, official Xinhua reported.
No casualties have been reported so far.
Crude liquid benzene is not water-soluble.
It can affect people's brain, skin, lungs and nervous system, the Xinhua report said.
