The students from China's Northeastern University were observing the flotation process at the mine in Inner Mongolia when the grid plate collapsed, sending them plunging into the tank, state news agency Xinhua reported.

All six were retrieved from the tank but pronounced dead by medical personnel, it added.

A teacher was also injured in the accident, which happened on Wednesday morning.

Mine safety in China has improved in recent decades, as has media coverage of major incidents, many of which were once overlooked.

But accidents still occur frequently in an industry where safety protocols are often lax.

Local authorities, the university and the owner of the mine, China Gold Group Co., "are handling follow-up work", Xinhua said.

A hashtag relating to the incident was the top-trending topic on social media platform Weibo on Wednesday night.

It had been viewed around 100 million times in the hour after Chinese media outlets published the news.

"The safety measures are not at all rigorous. What kind of company is this?" read one top-liked comment.