Six students from a university in China drowned Wednesday after falling into a flotation tank while visiting a mine in the country’s Inner Mongolia region.

The students from Northeastern University in Liaoning province were observing the flotation process when a grid plate they were standing on suddenly gave way, causing them to fall into the tank, according to Xinhua, China’s state-run news agency.

“Despite rescue efforts, all six students were confirmed drowned after being pulled from the tank. One teacher was also injured,” Zhongjin Gold, a subsidiary of state-owned China National Gold Group that operates the mine, said in a company filing Thursday.

Flotation tanks are used to separate different types of small mineral particles, said Richard Williams, principal and vice chancellor of Scotland-based Heriot-Watt University, who has a background in mineral engineering.

Anyone who falls into the tank could pass through the thick foam on top “and then find themselves in a mixed slurry or in contact with the mixer blades,” Williams said in emailed comments.

“These types of accidents are rare. But mine safety remains a global challenge due to the nature of the work,” he said.

Zhongjin Gold, which is listed on the Shanghai Stock Exchange, plunged at Thursday’s open and ended the day down 4.41%.

Calls to Northeastern University went unanswered on Thursday.

The flotation workshop had been carrying out technical upgrade projects, including replacing floor grating panels on the second-level platform to address on-site safety risks, according to an article that China National Gold Group Inner Mongolia Mining Co. published in February on its official WeChat account.

“In 2024, the flotation workshop achieved zero safety, environmental, or occupational health incidents, meeting the ‘zero accidents’ safety goal,” the article said.

Another article published in July 2020 described the flotation workshop during the summer as a “giant steamer,” where workers were drenched in sweat.

Both articles, which were viewed by NBC News, were deleted on Thursday afternoon after they were quoted by several media outlets.

The accident has been a top discussion topic on social media in China, which is one of the world’s top producers of many major minerals and has a long history of mine safety issues.

In January 2024, the Chinese government said it was introducing strict measures to “curb the frequent occurrence” of mining accidents. The previous year, there were 120 mine accidents in China resulting in more than 250 deaths, according to the country’s official Mine Safety Accident Network.

—NBC