Witnesses described seeing a "ball of flame" high above the sky and flames visible for kilometres after an explosion and fire ripped through the Lakeland Mills sawmill in the northern B.C. city of Prince George, killing one person and injuring 24 others.

Emergency crews rushed to the scene after the explosion engulfed the mill at about 9:45 p.m. PT, shaking nearby homes and businesses.

Flames at the sawmill, located about one kilometre outside the city, were reported to have shot more than 60 metres in the air at one point, according to witnesses.

The fire that followed has now been controlled but there are still hotspots and the fire isn't expected to be fully extinguished for another 24 to 48 hours, officials said Tuesday.

"There's nothing left standing as far as a recognizable physical structure. It was literally just a ball of flame," said Cameron Stolz, a Prince George city councillor.

All 50 workers who were on the job Monday night have been accounted for, officials said.

But on Tuesday morning, Northern Health spokesman Steve Raper confirmed one of the victims had died around 5:30 a.m. He was later identified as shift supervisor Alan Little, 43.

The fire at the Lakeland sawmill was largely out by Tuesday morning, but fire crews are still battling hotspots. (Marissa Harvey)

Twenty-four other people with varying injuries were treated at University Hospital of Northern British Columbia in Prince George, a Northern Health representative said.

"There were certainly some patients with some very severe burns, and we had to evacuate those to the waiting ambulances some distance away," said fire Chief John Lane.

A total of six people remained in hospital in Prince George in serious condition on Tuesday morning.

Three others in critical condition had been transferred by air ambulance to hospital in Vancouver and another person in critical condition was transferred to Edmonton.

Flames lit up downtown

Prince George Mayor Sheri Green said the news was devastating for the whole community.

"My thoughts and prayers and I know those of everyone is with every worker and with all of their families that are affected and for all of their emergency responders who are dealing with this as well. A fire and injuries from a fire are extremely difficult to deal with," said Green.

The fire chief said the sawmill, the log processing facility and the sorting facility were all destroyed, but the planer facility and an energy plant were intact.

The cause of the explosion and fire was not yet known and an investigation is expected to begin as soon as the fire is completely out.

The explosion shot a fireball about 60 metres into the air, according to witnesses. (Shannon Davies/Twitter)

Counc. Stolz told CBC News that he rushed to the scene after the explosion shook the house he was in.

"The flames literally lit up the entire downtown; they must have been visible for kilometres," he said.

The "cataclysmic" fire had many local families in shock, Stolz said.

Stolz said emergency services called in all the fire halls and extra staff, and extra workers rushed in to help at the local hospital.

Severe burns 'quite gruesome'

Co-workers at the Lakeland Sawmill scrambled to help each other immediately after the blast, with one saying he used scissors to cut charred clothing off those with severely burned skin.

"It was quite gruesome," said Brian Croy, first vice-president of the United Steelworkers Local 1-424 said from his home.

"When you walk out, there was guys with their skin hanging off their arms and stuff from being burned."

Croy said he was among six people in the mill's lunchroom talking about training when the explosion happened.

Suddenly the walls caved in and the room filled with thick smoke.

"That thing came up so fast, so quick. I don't know where it came from, but it was almost like a cannon going off. It blew through there. It ended just that quick," he said.

Croy said breathed through his jacket until the smoke cleared, then struggled to exit the burning wreckage.

"The smoke was just wicked, it took me down to my knees."

Workers scrambled to escape

Unfamiliar with the mill, and disoriented from the blast, Croy scrambled to get out with the others.

"There was flames coming up on that side, so we turned and headed the other way."

He and others ran down a set of stairs and crawled across some blown-down walls to get outside, where they found another man scrambling to escape.

The fire destroyed much of the Lakeland Mills sawmill in Prince George, B.C. (Andrew Johnson/Canadian Press)

"He was in really bad shape, his clothes were blown off, he was burned bad. The thing I noticed first off were his fingertips on both hands looked like they were gone."

Minutes later the men found the first aid tent, where Croy said he learned all the other workers were accounted for.

It's the second devastating explosion in B.C. in recent months. In January, an explosion tore through a mill near Burns Lake, killing two and destroying the mill.

The cause of that explosion has not yet been determined by investigators, who completed their investigation of the Babine Forest Products mill site just last week.

But some outside experts have pointed to high dust levels and limited ventilation at the Burns Lake mills as a possible cause.

With files from The Canadian Press. Time-lapse video by Morgan Andreychuk