The fire that destroyed a CN Rail trestle bridge in the community of Mayerthorpe, about 120 kilometres northwest of Edmonton, may have been purposely set.

"It is suspicious in nature," said Mayerthorpe fire chief Randy Schroeder on Tuesday.

"There were some witnesses that indicated people were in the area at the time of the fire."

Schroeder said there have been as many as 17 fires in the area over the last six days and all are under investigation.

The town's fire department were called to the scene of the blaze at 1:30 p.m. Tuesday along with employees from the rail company.

The fire is believed to have started on the ground near the base of the bridge. Almost three dozen firefighters from four different fire departments in the area were called to help douse the flames, alongside agriculture and forestry services members, helicopters and a water bomber, Schroeder said.

The loss of the bridge will impact the lumber and oil industries "extensively" Schroeder said.

Mayerthorpe resident Quinn White said the fire incinerated the bridge in just a couple of hours.

A before and after shot of the bridge. (Town of Mayerthorpe)

"When we got here, it was a relatively small fire," he said. "We could still feel it from across the tracks. Within an hour it was just engulfed in flames.

"Now the whole thing has just fell down and they're bombing it with water," he said. "There's some pillars from the truss still standing up, but for the rest of it, it's just all fallen down.

Dallas Bruneau-Fuhrer supplied this video of the fire-fighting efforts near Mayerthorpe, Alta. where a CN trestle bridge went up in flames Tuesday afternoon. 0:15

A trailer park with 38 mobile homes and nearby schools were evacuated, while some Lac St. Anne County residents living nearby were told to be ready to leave on one-hour notice.

The fire did not immediately threaten any homes as the wind was blowing away from the town, but officials wanted to be ready if the winds shifted, said town spokesperson Ashley Olsen.

Huge clouds of black smoke billowed into the sky during the fire.

The smoke from the blaze could be see from kilometres away. (Drew May)

There were no injuries. Town officials had urged residents to keep their doors, windows and vents closed, and to avoid the area.

Jamie Pond, who lives in a trailer park nearby, said she was prepared to quickly pack up her family's belongings and leave at a moment's notice.

I really thought I was walking away from my home today and I wouldn't see it again. And that's a tough thing. - Nearby resident Jamie Pond

There have been five fires in her area within the past week, she said.

"I really thought I was walking away from my home today and I wouldn't see it again. And that's a tough thing," she said. "The flames were very close, and I really thought, 'This is it.'

"We have been on edge because of the fires and stuff in this area. We've all kind of been on edge."

Pond said she's become angry about the recent fires in the area.

"Whatever is going on here, and I'm pretty certain these fires are being set, these people need to be brought to justice," she said. "This is not right."