A homeless man who died in a north Minneapolis house fire early Wednesday was killed by carbon monoxide poisoning after he started a fire to keep himself warm, the Minneapolis Fire Department said on Thursday.

The man, who has not been identified, was found unconscious on the first floor of the abandoned house on the 1400 block of Barnes Place after the fire was reported at 12:30 a.m. He was pronounced dead at the Hennepin County Medical Center.

The man was simply trying to stay warm and had built a fire on a bedroom floor. The bonfire weakened the bedroom floor, and two firefighters were hurt when they fell through the floor and into the basement, fire officials said. Their injuries were minor.

The department's community risk reduction officer, Casidy Anderson, urged people to call 911 if they suspect someone is living in an abandoned house.

Anderson distributed the following list of things to watch for that may indicate someone is living in a vacant/boarded building or house:

• Boards pulled off the window and/or door frames (on boarded-up buildings).

• Unconventional means of entering and exiting the structure -- such as through a window.

• Strange or unpleasant odors emanating from the structure.

• Different vehicles parked on or in front of the property.

• Lights on at different hours.

MATT MCKINNEY