Arson was blamed for a Calvert County house fire Thursday morning that damaged the structure but caused no injuries.

The fire, which took place about 9:50 a.m. in the 3600 block of Dory Brooks Road in Chesapeake Beach, was set in multiple places by one or more people who broke into the house and spread an "ignitable fluid," said Duane Svites, deputy chief state fire marshal.

Yvonne Sharon Mason, the only occupant of the house when the fire broke out, was in her basement apartment when she realized something was wrong.

"[She] heard people walking around upstairs, and she knew the occupant wasn't home so she called the sheriff for breaking and entering," Svites said. "Shortly after, she discovered the fire."

The house suffered about $75,000 worth of damage, according to an estimate by the state fire marshal's office.

Mason told Svites that her house had been broken into two years ago and then again two months ago and that many of her neighbors have been complaining about break-ins.

A small- to medium-size car was seen speeding away from the scene of the fire, but that is the only description connected to the arsonists.