The police said the number of missing persons has risen from six to seven after a massive fire broke out in a historic building in Old Montreal on Thursday.

Police and fire officials also added in a media briefing on Saturday evening that work to partially dismantle the building will begin Sunday morning.

They believe that victims will be found under the rubble.

"The second and third floors of the 15-unit building at Place d'Youville will be demolished 'stone by stone'," according to Martin Gilbolt, Montreal fire chief.

But to this day, firefighters have not been able to enter the building due to safety concerns.

Gilbolt also said the partial demolition will be done slowly to protect workers and preserve the building's heritage.

Montreal police arson commander Steve Belzil said it is too early to say whether the fire was criminal or intentional.

Belzil also said the building owner is cooperating with investigators to clarify the circumstances of the fire and provide necessary information.