Local police have detained an unspecified number of people who were found accountable for a sewage tank collapse in Haining, Zhejiang province, which killed nine and left another four severely injured.

The accident occurred at around 5:35 pm on Tuesday at a printing and dyeing mill, according to the local government and the rescue team.

All 22 of the people who were missing were found by 2:30 am on Wednesday.

The collapse of the 15-meter-high tank, with a diameter of 3 meters, toppled stacking shelves in a five-story workshop in the mill.

The injured have been sent to nearby hospitals for treatment.

The accident scene is being cleared and further investigation is underway, officials said at a news briefing on Wednesday morning, adding that the Haining government is undertaking a thorough check on hidden safety hazards of local printing and dyeing enterprises and other high-risk industries.

When asked if the leaked sewage would harm the local environment, Wang Jiankun, deputy Party chief of Haining, said the environmental protection administration is investigating that possibility and the water quality of rivers nearby is being tested and monitored.

The mill company－Haining Longzhou Printing and Dyeing Co－was founded in 1997 with a registered capital of 14.6 million yuan ($2.08 million) for the production, printing and dyeing of textiles.

Haining, located in Jiaxing in northern Zhejiang, has long been dubbed China's fur and leather production and trading hub. The county-level city is home to about 1,500 leather and fur production enterprises. Haining China Leather City, covering 1 million square meters, is home to over 6,000 trading entities, with annual sales volume surpassing 20 billion yuan.

Qin Jirong and Xinhua contributed to this story.