Radioactive emissions 50 times higher than normal have been detected in waters close to a nickel and zinc mine in central Finland after a pool holding contaminated water was damaged, nuclear safety agency STUK and Finnish media said Friday.

In a statement, STUK said the elevated levels of uranium posed no human health risk, but the mine operated by Talvivaara has indefinitely suspended operations while it cleans up.

The radioactivity was detected following a breach Sunday in a water basin used during mineral extraction. Finnish public radio Yle said water had escaped containing residues of nickel and uranium.

Talvivaara confirmed the breach was the source of uranium. The firm said most of the escaped liquid had been contained by safety dams, but said some water had escaped from the mining area.

Greenpeace said the bottom of a waste pool had ripped, causing massive leaks.

"The heavily contaminated water started spewing out at a rate of thousands of cubic metres every hour," the environmental group said, noting that other leaks had previously occurred at the mine.

"Nobody can tell yet exactly how bad the situation is," Greenpeace added.

Operated by the Talvivaara Mining Company, the mine is located in the Kainuu region, more than 550 kilometres (340 miles) north of Helsinki.

The facility produced some 10,600 tonnes of nickel and 21,800 tonnes of zinc during the first three quarters of the year.