Death toll has risen to nine in a sewage tank collapse at a printing and dyeing mill in east China's Zhejiang Province, Xinhua news agency reported, quoting local authorities on Wednesday.

The accident occurred at around 5.35 pm on Tuesday in the Haining Longzhou Printing & Dyeing Co., Ltd. in the city of Haining. 

Four people were severely injured and are under treatment in hospital, according to a municipal government spokesperson.

More than 500 rescue workers and 30 vehicles had joined the rescue search operations, the spokesperson said.

Local government has launched an emergency plan to treat pollution and monitor the water quality of nearby rivers.

The cause of the accident is under investigation.

- Bernama