A gold mine closed down for failing to comply with regulations earlier this year has been shut again after inspectors found it was still operating.

The Broken Hills underground gold mine in the Coromandel has been issued with a prohibition notice by the Department of Labour's High Hazards Unit until it develops a plan for a second exit from the mine.

Gavin Taylor, the acting chief mines inspector, had shut the mine in February for not complying with mining safety regulations.

Mr Taylor said the mine's operator was required to provide a plan for a second exit from the mine before it could reopen.

"He has not provided us with that plan, so my requirement that the mine is not worked is still in force."

He said two inspectors went to the mine on Thursday and found it operating and also potentially breaching other mine safety regulations.

"I had no option but to order the mine shut down until the owner provides the High Hazards Unit with a plan for developing a second exit for safety assessment," Mr Taylor said.