Montreal fire officials now say at least six people are missing after a blaze destroyed a building in the city’s historic district Thursday.

Investigators had initially said one person was believed to be missing after the fire that injured another nine people.

Montreal fire operations chief Martin Guilbault says information recently confirmed from various sources led them to conclude more people were trapped inside when the fire broke out before 6 a.m. Thursday.

The cause of the fire remains unknown, and Guilbault told reporters that the investigation is being led by the Montreal police arson squad.

Fire officials say two of the nine injured people suffered serious burns and remain in hospital.

Montreal fire Chief Richard Liebmann said Thursday there was some confusion over how many people were inside the three−storey Old Montreal building at the time of the fire because several apartments were Airbnb rentals.