The cause of a fire that injured 26 people in a Bronxdale apartment building is under investigation Monday.

Fire officials say the fire broke out Sunday as a family was putting up its Christmas tree in an eighth-floor Boston Road apartment. The Kalaj family, which includes three young children, was able to escape.

Eleven firefighters and several tenants were treated for smoke inhalation. Officials say one person was taken to a hospital in cardiac arrest. There is no word on that tenant's condition.

The fire charred the apartment and left neighbors' carpeting soggy and their walls full of soot.

Officials do not know what caused the blaze.