Six university students drowned on Wednesday while on a field visit to a copper-molybdenum mine in northern China, owned by Shanghai-listed Zhongjin Gold Corp.
The students from Northeastern University in Shenyang fell into a flotation cell - a piece of mining equipment that uses a liquid solution to extract copper from crushed ore - after protective grates collapsed.
A teacher was also hurt in the accident at the mine located in China's Inner Mongolia region, according to a stock exchange filing from Zhongjin Gold, a subsidiary of state-owned China National Gold Group Co.
The company said it activated an emergency plan and reported the incident to the relevant departments of the local government.
The operator of the mine, a subsidiary of Zhongjin Gold, halted production, the company said in another stock exchange filing later on Thursday.
Such field visits have been organised for years and the incident was unexpected, said a teacher from Northeastern University, according to a social media account belonging to Henan Radio and Television.
The university sent staff to the site to manage the incident, the teacher said.

At least six people die in coach fire in Switzerland
Trump says US destroyed mine-laying vessels after warning Iran
Britain working with allies to support shipping through Strait of Hormuz
Five Iranian women's soccer players granted humanitarian visas in Australia
Almost 700,000 displaced after Israeli strikes on Lebanon, UN agencies say
Iran fighting back but not stronger than U.S. thought, top U.S. general says
British warship HMS Dragon departs for Eastern Mediterranean
One dead, several injured in Iranian attack on Manama building
