CN (TSX:CNR) president Claude Mongeau described the fire as a controlled burn that is normal after a derailment involving cars carrying petroleum products.
He said 17 of the train's 122 cars derailed near Wapske and five of them were carrying crude oil from Western Canada that was destined for an Irving Oil refinery in Saint John, N.B. Four other cars were carrying liquefied petroleum gas.
"We don't have a lot of information, we are assessing as we speak," he told a news conference in nearby Plaster Rock. "The impact on the environment, air quality, spill seems to be very contained and hopefully will be manageable.
"The fire is our first priority at the moment. We have the equipment, we have the people and we have all the procedures in place to deal with it in a safe manner."
Late Wednesday, the company said two of the cars carrying liquefied petroleum gas and one car carrying crude oil were on fire.
Aerial images of the derailment showed a jumble of cars strewn across the tracks in a wooded area with fire and smoke billowing from the wreckage.
New Brunswick's Emergency Measures Organization said there have been no injuries and the number of people affected by an evacuation has climbed from about 60 to 150 people. The Health Department said as a precaution, people in the area with private wells should not consume their water.
The regularly scheduled freight train ran into trouble about 150 kilometres northwest of Fredericton at about 7 p.m. Tuesday.
CN spokesman Jim Feeny said the only people on board the train — the conductor and engineer — have provided statements, but he wouldn't reveal what that they said. He added that no one was injured.
The province initially ordered the evacuation of an area within a two-kilometre radius of the fire Tuesday night, but officials said no one was using an evacuation centre set up by the Red Cross as people forced from their homes found places to stay with family and friends.
Feeny said some residents were allowed to temporarily return to the homes Wednesday to briefly check on pets and the condition of their residences. But as of late Wednesday, the fire was still burning and it was unclear how long it would take before it burned itself out, he said.
"On a controlled basis, we and the local authorities are allowing local citizens access to their properties," he said. "It's an in and then out kind of thing."
Rail safety has become a major issue across the country since the deadly derailment in Lac-Megantic, Que., last summer and as a growing amount of fuel oils and crude petroleum is carried by train across the country.
The federal Transportation Safety Board has sent investigators to the scene of the derailment and based on preliminary information from the company and the RCMP, it said the train's brakes came on unexpectedly.
"The preliminary details that we received indicate that while the train was proceeding it had experienced an undesired brake application," Daniel Holbrook, manager of head office and western regional operations for the safety board, said from Gatineau, Que. "The train then came to a stop."
He said the crew went to inspect the train and found that the 13th car behind the locomotives had derailed and noticed the axle had failed, but investigators don't know what role that might have played in the derailment. Holbrook said investigators don't yet know the sequence of events and what car derailed first, which they will be looking at.
On the train is a continuous pipe that supplies air to the brake systems on all of the cars and locomotives, Holbrook said, and if that pipe breaks it applies the emergency brake.
"So as this train was proceeding there was presumably a break in the brake pipe and the brakes came on and the train came to a stop," he added.
Mongeau said the train was inspected in Montreal as per regulation before it left that city and that it would have moved over a number of wayside detectors designed to identify potential problems such as mechanical issues with wheels or dragging equipment. He said officials would want to review the data from those detectors.
Andrew Simpson, 30, lives on a road right next to the derailment and was playing cards with his uncle when the train went off the tracks.
"The table just kind of rumbled and out the window went a real bright orange," he said. "We looked out and the whole train yard was on fire. We panicked and called 911."
He said he and his uncle quickly left the house and tried to alert people to get them out of their homes. He could see lumber and one tanker burning, adding that he was about 100 metres from the site of the derailment.
Simpson said he couldn't smell anything and that there was no warning of trouble prior to the table rumbling.
Asked if he ever had concerns about the rail line, he replied: "No, everything has run smooth until yesterday."
Steve Legace, a resident of Plaster Rock, said tensions had calmed considerably since Tuesday evening when many didn't know the extent of the risk.
"It's kind of unnerving, I guess, knowing that we have things that close going through our village and not knowing what's being carried on these vessels," he said Wednesday. "Things seem to have calmed down and people are not as upset as they were and a little more at rest now."
While in Inuvik, N.W.T., Prime Minister Stephen Harper defended his government's record on rail safety and inspections, saying it has boosted spending in those areas "vastly." He said the government will look at any recommendations that may come from the Transportation Safety Board.
"We will take whatever further steps are necessary," he said.
Premier David Alward said the derailment doesn't undermine his confidence in the safety of transporting dangerous goods by rail.
"Goods move every day, whether that be by roads or by rail, pipelines or by air. There are always risks," he said.
"What we need to make sure is that the systems are safe ... and that when something happens we have the ability to respond quickly and effectively."
New Brunswick's Emergency Measures Organization said it was notified of the derailment Tuesday around 8 p.m. Hazardous materials crews were dispatched and the site has been secured by the RCMP.
Note to readers: This is a corrected story. A previous version said four cars were carrying liquefied propane gas.