A mother and her child escaped a burning duplex in Castle Shannon early Thursday morning thanks to a neighbor who spotted the flames.

Firefighters said the blaze started just before 5 a.m. at a home on Cooke Drive. Officials said the fire began in a vacant part of the duplex but quickly spread to where a family was sleeping.

A neighbor said he was walking by the house, spotted the fire and alerted the mother and her son.

"Some guy started knocking and said, 'Fire!' So my mom woke me up and said there was a fire. So I started crawling down the stairs and I came outside," said Ben Honsinger.

Another neighbor said he witnessed the man pounding on the family's door.

"God sent an angel. He was pounding on the door and got her out and her son out in time because it spread pretty quickly," Graham said.

The Castle Shannon fire chief said the roof collapsed while crews were working to extinguish the fire. Two firefighters were inside at the time of the collapse and one was hurt –- but is expected to be OK.

"There's a good chance that if this person going to work hadn't stop or didn't see it early enough we would have had another situation here," Castle Shannon Fire Chief Bill Reffner said.

Investigators said the fire most likely started because of an electrical problem.