Fires believed to have been set just weeks apart in at least 10 vacant homes, garages, or abandoned buildings in Southeastern Massachusetts have raised concerns that an arsonist could be on the loose.

Hours after determining that two fires within 2½ miles of each other in Plympton and Halifax were set early Monday, state Fire Marshal Stephen D. Coan’s office said evidence suggests that some of the fires set in the past month are connected, and authorities are investigating whether all of them may be linked.