Dozens of miners were trapped underground at a platinum mine in southern Zimbabwe on Tuesday after a fire, the mine's owners and a union leader said.

Implats and Aquarius Platinum, the joint owners of Mimosa mine in the small town of Zvishavane confirmed the accident which occured overnight.

The company said there were 75 employees underground, but unions said there were 85 at the time of the accident.

"All employees have been accounted for and no injuries have been reported," the company said in a statement.

The workers were being moved to the surface on Tuesday, it said.

"A conveyer belt collapsed and caught fire yesterday (Monday) at around 17:00 hours (1500 GMT) trapping 85 workers underground," Shadreck Polowelo, president of the Zimbabwe National Mine Workers Union told AFP by phone, adding that at least 20 had been rescued.

The fire, which has been extinguished, was caused when a conveyer belt "ignited".

Polowelo said "20 have been rescued and rescue efforts are continuing."

Mimosa platinum mine is situated in Zvishavane, about 390 kilometres south of the capital Harare