LAC-MEGANTIC, Quebec — Hazardous conditions hindered firefighters’ attempts today to search for some 40 people still missing after a runaway oil tanker train exploded early Saturday morning, killing at least five people.

Quebec provincial police Sgt. Benoit Richard said there was no searching overnight because the situation remained too dangerous.

He said only a small part of the devastated scene has been searched.

Many of those missing were believed to have been drinking at a popular downtown bar when the explosions occurred and rescuers were still not able to reach the area, Richard said.

Firefighters today were focusing their efforts on two oil-filled cars dousing them with water and foam in an attempt to keep them from overheating and exploding.

All but one of the train’s 73 tanker cars were carrying oil when they somehow came loose, sped downhill nearly seven miles into the town of Lac-Megantic, near the Maine border, and derailed, with at least five of the cars exploding.

About a third of the community of 6,000 was forced from of their homes by the explosion and flames.

Joe McGonigle, Montreal, Maine & Atlantic Railway’s vice president of marketing, said the company believes the train’s brakes were the cause. “The train was parked, it was tied up. The brakes were secured. Somehow it got loose,” he said.

McGonigle said there was no reason to suspect any criminal or terror-related activity.