At least five people died and 40 were missing after a runaway train carrying crude oil derailed and exploded in the center of a small Canadian town in a disaster that raised fresh questions about shipping oil by rail. The train, which did not have an engineer aboard when it derailed, was hauling 72 tanker cars of crude from North Dakota to eastern Canada. It rolled downhill from an overnight parking spot, gathered speed and derailed on a curve in the small town of Lac-Megantic. Each car carried 30,000 gallons (113,000 liters) of crude oil. Four caught fire and exploded in a orange and black fireball that mushroomed hundreds of feet into the air and flattened dozens of buildings, including a popular bar. "It looks like a war zone here," said Canadian Prime Minister Stephen Harper, who visited the town on Sunday. "This is an unbelievable disaster. ... There isn't a family in this area that is not touched by this, that is not affected by this." Montreal, Maine & Atlantic, which owns the line, said it was investigating the cause of the accident, but the release of the train's brakes might be linked to how the locomotive was shut down in the nearby town of Nantes. Police spokesman Michel Brunet said five people died and about 40 people were missing. He also said police were keeping all options open as they investigated the disaster. "Every time the Surete (Quebec police) needs to investigate, we need to rule out any foul play," police spokesman Benoit Richard told reporters. "Right now, we cannot say it is a criminal act. We can only say we are looking at it as if it was." Nantes Mayor Sylvain Gilbert told local radio that town firefighters had dealt with a fire on the train when it was parked in the town on Friday night. It was not clear if that fire was connected in any way to the derailment, or why the train became unsecured in Nantes. Montreal Maine & Atlantic said the engineer had secured the train in Nantes and left. It said the locomotive was subsequently shut down, "which may have resulted in the release of air brakes on the locomotive that was holding the train in place." The company's statement did not mention a fire or explain when the train was shut down and company officials could not be reached to comment further. Canada's Transportation Safety Board said the brakes would be a focus of the investigation it has already started. "Certainly, the manner in which the train was secured, both hand brakes and air brakes - we'll be looking very strongly at that," chief investigator Donald Ross told reporters. He declined to comment on Montreal Maine & Atlantic's statement. Montreal Maine & Atlantic is one of many railroads that have stepped up shipments of crude oil as pipelines from North Dakota and from Canada's oil producing areas fill to capacity. Bar Patrons a Concern On Sunday, white vapor still rose from the town center, which police have cordoned off. Photos showed shattered buildings, burning piles of rubble and stumps of burned trees. Very few people were treated in hospitals, indicating that those caught in the blast had either escaped or died. "It is a black-and-white situation," Quebec Health Minister Rejean Hebert told reporters. Residents said they were particularly concerned about people who had been inside the Musi-Cafe bar, a popular night spot located next to the center of the blast. "There was a big explosion, the heat reached the cafe and then a big wall of fire enveloped the road," said Bernard Theberge, who was sitting on the patio of the restaurant as the train barreled into town. "There were people inside. I thought for maybe two seconds that I should go in, but the heat was too strong to get to the door." Lac-Megantic, a lakeside town of 6,000 ringed by forests of pine and birch, is in the predominantly French-speaking province of Quebec, about 160 miles (255 km) east of Montreal and close to the border with Maine and Vermon