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Railway ties were on fire on the entire stretch of a CN Rail bridge south of Lytton, B.C., Thursday. Joelle Harvey (Joelle Harvey)

CN Rail hopes to have a company rail bridge damaged by fire on Thursday back in service sometime this weekend.

According to one witness, the fire lit up the Fraser Canyon bridge from end to end, burning railway ties and emitting a billowing cloud of black smoke.

While the bridge remains structurally sound, officials say the damaged ties need to be replaced.

CN spokesman Jim Feeney said more than 50 people are working around the clock to get the steel bridge back in service.

"It's an important bridge, it's our transcontinental mainline," Feeney said.

"It's the link between the Port of Vancouver and the rest of our North American network. It would see in the range of about 30 trains a day."

Feeney said the cause of the fire is under investigation.

In the meantime, he said all freight and passenger rail traffic is being rerouted along an adjacent CPR line.

With files from The Canadian Press