An explosion and fire at a refinery in north Regina forced 1,400 people from the facility, and sent seven to hospital with burns.

Two others were treated at the facility owned by Consumers' Co-operative Refineries Ltd.

At 8 p.m. CST, Vic Huard, the vice-president of corporate affairs at Federated Co-operatives Ltd., told CBC News four people had been released from hospital. Of the three still there, one is in critical condition, one in serious-but-stable condition, and one has an unspecified fracture.

All of the injured were contractors working on a $1.9-billion renovation and expansion of the refinery.

When the explosion took place, there were 450 day staff and nearly 1,000 contractors on site.

Worst fire in 20 years

Witnesses told CBC News that the fire began after a large explosion in the diesel processing area of the facility at around 2 p.m. CST.

One worker said that after the explosion, he saw a giant fireball that was so hot it melted steel.

Emergency crews battled the fire as flames and black smoke shot into the sky.

The Consumers' Co-operative Refinery in Regina was evacuated because of a fire that followed an explosion at the facility. (Jordan Jackle/CBC)

There were concerns that the fire could spread and ignite gas and diesel tankers on the other side of the facility.

Shortly before 3 p.m., the fire was under control.

Refinery officials said there is no danger to the public.

They said they have found the ignition point of the fire, and suspect the cause was a pipe leaking a mixture of hydrogen gas and diesel fuel that found a spark.

It was the worst fire at the refinery in 20 years.

The fire has reduced the facility's diesel production ability by about 25 per cent, but has not affected its gasoline-processing operation. The refinery processes 100,000 barrels of crude oil in a day. The expansion is expected to increase that to 130,000 barrels per day.