MONTREAL - About 250 firefighters did their best to extinguish a fire at a building under construction in Rosemount, but were unable to prevent the fire from spreading to six nearby buildings.

The fire began around 3:30 a.m. Tuesday on Dandurand Rd. between 9th Ave. and 10th Ave.

"When firefighters arrived other buildings were threatened, so our first priority was to evacuate those other buildings," said Denis Doucet of the Montreal Fire Department.

They rushed through nearby buildings and ordered 70 people into the street.

"They were knocking on doors, getting people out really fast, screaming 'Fire, fire, fire!'" said Kathleen Beaudin.

Ivan Arnold was one of the first people woken up by the fire.

"I went back to my balcony, opened the door, and there were huge flames coming up to us, and after that there was a little bit of panic," said Arnold, who then grabbed his children and ran from his home.

By 6:45 a.m. most of flames were out, but there were still several hotspots and a considerable amount of smoke and steam rising from the burned-out wreckage, with fires sparking up again as covered areas were exposed to air.

While nobody was hurt, six neighbouring buildings were damaged by flames, and some will have to be demolished.

"Buildings under construction do not have any smoke detectors, so fires can spread very quickly before anyone notices," said Doucet.

Investigators from the fire department and, as is customary for buildings that burn under construction, the Montreal Arson squad will be at the scene throughout the day trying to determine how the fire began.

The leading theory is that propane tanks stored on the construction site exploded.

"We are in wintertime and that's the kind of heating system they used, so many bottles of propane were on the scene," said Doucet.

At least one expert says he has never seen a fire of this magnitude.

"I've never seen this big," said Jerome Drapeau of Qualinet Nettoyage. "I've talked to residents in this area, people who have been here for more than 50 years, and they've never seen this big."

The Red Cross has been sheltering people displaced by the fire, and will help them in finding places to stay for the next few days. Sun Youth volunteers also arrived on the scene to assist the 70 evacuated people, who were given shelter at the Centre Etienne Desmarteaux.

While about a dozen people have lost their homes, the rest should be allowed to go home in a few days.