Workers at a Saskatchewan potash mine have returned to the surface after spending a day underground in a refuge area, following a fire that broke out in the early hours of Tuesday morning.

The fire was extinguished earlier in the day, but the workers could not return to the surface until air quality tests showed it was safe.

Fifteen workers were in the first group to surface around 7 p.m. CST, a journey that took about 45 minutes.

The last of the miners surfaced around 8:30 p.m.

"I think I'm going to go and have a cold beer," Darwyn Wirth told reporters shortly after he and his colleagues were brought safely back to the surface.

Potash mine workers head for home after spending a day in an underground safe room following a fire. (CBC)

The fire started at 1:56 a.m. on Tuesday at PotashCorp's Rocanville mine, according to the company.

The miners were able to communicate with the outside and were not in immediate danger, said PotashCorp manager of public affairs Bill Cooper.

No one was injured in the fire, he added.

After they were safe, the miners explained that when the fire alarm sounded everyone immediately headed to four separate refuge stations scattered throughout the facility.

"We have an alarm system with loud bells and flashing red lights, and you immediately go to a refuge station and call the control room so they know where you are," said Wirth.

Rocanville, Sask., where the potash mine is located, is close to the Manitoba-Saskatchewan border, about 230 kilometres east of Regina. (CBC)

It took about 10 hours to extinguish the fire, but it took several more hours for crews to determine it was safe to bring the workers up.

"It's a matter of cooling the area down and ventilating the air," Cooper added. "There's kilometres of tunnels underground and just the way the ventilation system works, it's got to clear all that out. The air quality's got to be at a point where it's safe to take people to the surface."

Kept in safe room

The rooms where the workers waited were described as comfortable, though not really posh.

"There's no place to sleep," Wirth said. He laughed when told another group had passed the time by playing cards.

"We didn't have a deck of cards. We really would have liked a deck of cards."

One of the trapped workers was Ben Mitchell, a 26-year-old mechanic from Birtle, Man.

Mechanic Ben Mitchell, 26, was in the safe room since early Tuesday morning, according to his fiancee, Nicole Lane. (Facebook)

His fiancée, Nicole Lane, told CBC News that Mitchell called her at around 7:45 a.m. using a phone in the safe room.

"He called and just said that he was safe in there, that he was in there by himself because nobody was … working with him at the time," she said.

"The mine would be calling him every hour to make sure that he was OK."

Originally, there were 29 people underground when the fire broke out, but nine of them were lifted out.

The cause of the fire hasn't been disclosed, but it started when a large wooden spool somehow ignited, Cooper said.

The Rocanville potash mine is about one kilometre below ground, but tunnels from the main shaft spread out horizontally for about 16 kilometres.

"Our task was once we find out that there is an emergency, the protocol is to get ahold of all our guys," explained mine rescue supervisor Courtney Ryan of Tantallon, Sask.

"We also talk to Mosaic Potash and if we need any of their help, they support us."

Worry over smoke

He said the fire is not what poses the greatest threat.

"Smoke is the worst thing that can happen underground. If you don't have your fresh air and exhaust separated, smoke goes where it's not supposed to go and people can become engulfed by smoke.

"We had enough ventilation so that the smoke didn't back up too far so we were able to approach the fire within 20 to 50 feet. It was nice to get it done and the guys home."

Rocanville is about 230 kilometres east of Regina.