Fire broke out Sunday in a mine in central Canada, forcing some 70 miners trapped underground to retreat to emergency rooms with oxygen and supplies, a mine official said.

Marshall Hamilton, a spokesman for Mosaic Company, the Minneapolis-based firm that operates the potash mine, said the fire broke out around 3 a.m. nearly a mile underground in the province of Saskatchewan.

The miners reported smoke and headed for safe refuge rooms where they waited for firefighters to put out the blaze and for air quality in the mine to improve.

"In those refuge stations, they can seal themselves off and there's oxygen, food and water," Hamilton told CBC Radio. "And they can stay in there for at least 36 hours."

Hamilton said company officials had not been able to establish a radio link with 30 of the miners, but that there was "no reason to doubt they are anything but safe."

"We are in regular contact with approximately 40 of them," he told CTV News. "There are 30 of them that are in an area where the communication link, we believe, was destroyed by fire, so we believe they're safe."

Teams of rescue workers were been going into the mine for a few hours at a time, beginning about 5 a.m.

Hamilton said they believe they have found the source of the smoke and were working on extinguishing the fire. He said the mine would be cleared of smoke and toxic gas before workers would be brought out, adding "we'd rather do this safely than quickly."

"We'll go get them when we're absolutely confident that the fire is out and the smoke and the toxic gases that are associated with fires have left our operations and the air is safe for them to breathe," he said.

He said that some of the miners' families had gathered at the mine.

"They're a little bit tired. They're a little bit anxious. They have confidence that we've going to safely bring them up," he said. "Nevertheless, they'd like to see them sooner rather than later."

Potash is a pinkish-grey mineral used in the production of agricultural fertilizer.