INDIANAPOLIS -- Indianapolis fire investigators blame the cold weather for a rash of blazes set at abandoned homes.

Firefighters have responded to 20 such fires in the last month, the latest Friday night on the city's east side. Capt. Rita Reith said all of the blazes were likely set by homeless trying to stay warm.

"They'll use whatever available materials they have, whether it's newspaper clothing, a mattress that's left by somebody else, wood from outside. They'll bring it in," she told 6News' Sarah Cornell.

Reith said warming fires are especially dangerous because, unless someone notices the flames, they spread quickly, and she's concerned they will only become more common as temperatures drop.

"The shelters reach capacity rather quickly, or the residents don't want to go to the shelter because they may have rules or other limitations placed on them while they are at the shelter," she said.

During the winter months, downtown's Wheeler Mission changes its protocol to ensure as many homeless as possible can seek shelter. Anyone is allowed in, and if they don't have enough beds, they set up extra on the floor.

Fire officials ask anyone who notices suspicious behavior around a vacant house to call Crime Stoppers at 317-262-TIPS.