Fire crews assess the smouldering remains of a Prince George fire Tuesday morning. (Betsy Trumpener/CBC)

Provincial officials were monitoring the environmental effects of three major fires that erupted Monday evening in an industrial district of Prince George, B.C.

The fires continued to smoulder through much of Tuesday morning, but Jim White, director of operations for the Provincial Emergency Program, said just before noon that the Prince George fire department had the remains of the blazes under control and the threat of further spread had been reduced.

A state of emergergency was declared by Mayor Colin Kinsley until the fire was under control late Tuesday afternoon.

PEP officials were notified Monday night that the fires posed a potential hazardous materials risk and Ministry of Environment staff were dispatched to monitor the situation.

"The main concern is that run-off from the water being used to douse the fires could run into ditches and could enter the nearby Fraser River," White said.

A fire truck douses the remains of one of three fires that burned in the Prince George industrial district Monday night. (Betsy Trumpener/CBC)

"There's always going to be some hazmat [hazardous materials] issue with the water running off from the fire," he said.

"A number of creosote piles were burning, and things like that. When you pump a significant amount of water in an industrial park, you get a lot of water washing through the fire site that's going to wash debris down into the ditches."

Prince George Fire and Rescue crews' efforts minimized the threat from volatile chemicals stored near the burning warehouse, city officials said.

The Ministry of Environment said investigators would also be in the fire zone today to test air quality after people in many parts of the city woke up to find the air filled with heavy smoke and ash.

“Anyone with respiratory challenges would be advised to stay inside today and allow the firefighters to get the fires out, so no more smoke is being emitted. Let the breezes carry the particulate, clean that out, and provide as clean air as we possibly can,” said Kevin Brown, a spokesman for the City of Prince George.

Fires started at plywood mill

The first fire started early Monday evening at Canfor's North Central Plywoods plant, destroying that facility.

Workers said the blaze appeared to have started in one of the plant's three veneer dryers but quickly spread across the roof.

Crews managed to control that blaze by late Monday night but sparks ignited material at a warehouse in a B.C. Rail industrial area, nearly two kilometres away, destroying that structure early Tuesday morning.

Brown said in addition to the fires at the Canfor site and at Interior Warehousing, a pile of railway ties also burned through the night.

"They are part of the CN Rail maintenance yard and as one would expect with wooden, treated rail ties, those are very volatile."

Firefighters were also called to a fire in the downtown core of the central B.C. city at dawn, but quickly doused the flames in a dumpster. Authorities believe the fire, which spread to a nearby lighting store and caused significant damage, was deliberately set.

The fires stretched the resources of city staff and Brown called it "truly remarkable" that there were no reports of serious injuries.

"We knew through most of the evening there was hot embers blowing in the wind, spreading for a distance of up to three kilometres," he said.

"A state of emergency was declared at 1:30 this morning," Prince George city spokesman Kevin Brown said Tuesday.

"Of course that was put into place to allow the Prince George fire and rescue members to haul in extra resources if they had needed them.

"The state of local emergency would have also helped in case the area needed to be evacuated but there has not been an evacuation."

The damage to the city, which is already reeling from a severe downturn in the forest industry, may be felt for some time.

"It would be safe to say over 300 people are out of work this morning because of the fires," Brown said.

He called the situation the largest combined fire incident in city history.