A large area of the Plateau district remained shut off to traffic Wednesday following a fire that police say is suspicious.

Officers released a man who was held in custody Wednesday afternoon after the fire broke out in a building under construction at St-Andre and Roy around 8:50 p.m. Tuesday. They say he was not involved in the fire after initially bringing him in to question him. Witnesses said he was acting suspiciously around the site of the blaze.

Some 150 firefighters battled the blaze, which destroyed six duplexes and triplexes as well as a number of vehicles. Two buildings collapsed, another two might have to be demolished and two more will have to be rebuilt. A seventh building was damaged during the firefighting operation.

Witnesses say the fire spread very quickly.

"It caught on fire, boom!" one woman told CTV News.

"It was all red and yellow and everything."

Another man said the flames were at least three storeys high.

"I didn't even turn off the computer," he said.

"I just fled the house and started ringing the doorbells for everybody to get out."

Homeless

Hundreds of people from 14 units were forced into the street. Thirty of them are now homeless and some of them slept in a nearby park while others were put up at hotels.

The Red Cross is helping some of the victims.

None of the residents was injured, though three firefighters were treated for heat exhaustion as temperatures approached 30 degrees C.

The block between Napoleon, Mentana, Cherrier and St. Hubert streets was off-limits as investigators and firefighters combed the rubble, which was still smouldering 12 hours after the fire broke out.

Tupper St. Fire

A fire in a vacant building caused a commotion in the western edge of downtown on Wednesday morning.

It broke out at around 3:30 a.m. in a four-storey building on Tupper street.

Nearby residents had to leave their apartments as did guests at the Hotel Fort.

No one was injured.