(CNN) -- At least two firefighters died when they were shot at the scene of a blaze in upstate New York on Monday, police said.
Two other firefighters were injured, police in Webster, New York, told reporters.
Authorities believe one or more shooters took aim at the firefighters after they left their vehicles, Police Chief Gerald Pickering said.
It was unclear whether there were any suspects.
"We have different individuals that were possible people with knowledge, but at this point I can't really comment," Monroe County Sheriff Patrick O'Flynn told reporters.
For hours, the gunfire stopped firefighters from working to extinguish the fire and forced police SWAT teams to evacuate homes in the area.
Firefighters first arrived before 6 a.m., said Rob Boutillier, Webster's fire marshal. By 9 a.m., flames had engulfed three houses and a vehicle, he said.
"It's still an active crime scene," Pickering said. "We have firefighters there at the location. It took a while to make it safe ... to put out the fires."
Doctors were treating the wounded firefighters Monday morning, said Teri D'Agostino, a spokeswoman for Strong Memorial Hospital in Rochester, New York. They were in guarded condition, she said.
One firefighter escaped from the scene in his own vehicle about an hour after he was shot, then was taken to the hospital by an ambulance from another location, Boutillier said. He was listed in satisfactory condition, Boutillier said.
Another wounded firefighter was conscious and speaking when he was removed from the scene, Boutillier said.