The company will use a helicopter to search for the leak on Wednesday morning. The aim is to assess the direction of water flow through an aerial view.

“We are hoping to find the exact place of the leak within a few hours -- over the course of today,” said Talvivaara Head of Communications Olli-Pekka Nissinen on Wednesday.

He stressed that most of the waste water has been collected in a backup pond to the south of the mine, where a fourth dam will be completed by the weekend.

"A significant amount of waste water has not leaked beyond the mine," he said.

Talvivaara will decide on Wednesday whether or not to restart production at its metals plant on the site. Nissinen said it is possible to reopen the plant without disturbing rescue operations at the gypsum waste pond.