Industrial chemicals that leaked into a river, leading to water supplies being cut last week to 30,000 residents in suburban Shanghai, exposed faults in the supervision of chemicals' production and transportation, an expert said.

The leak, caused when a valve being used to control discharge from a tanker to another vessel was left open, also highlighted low access to the chemical manufacturing industry, the expert added.

"It should not be as easy as a company paying some money, and then getting a plot in a chemical enterprise park and starting production," said Dai Xingyi, a professor at the Department of Environmental Science and Engineering at Fudan University in Shanghai.