YAKIMA, Wash. — Authorities say a string of fires reported since Sunday — including three within three hours this morning — are “definitely suspicious.”

Most of the four structure fires, either garages or houses, apparently were started from the outside. Fire appeared heaviest on the alley side of the buildings at some of the scenes, investigators said.

That’s a good indication that people started the fires, said deputy city fire marshal Ron Melcher, though there’s no clear indication whether a single person or a group might be responsible.

The fires remain under investigation. Anyone with information about the cases may call 800-55-ARSON or 509-575-6140 to make a confidential report.

In the latest of the house fires, a firefighter suffered minor injuries when he fell through a floor at a house fire early this morning, officials said.

One of the three residents had to be escorted out of the burning house; the other two left safely on their own, according to a news release from the Yakima Fire Department.

The 3 a.m. fire in the 1300 block of Garfield Avenue was the last of three fires to which the fire department has responded since midnight Tuesday.

The others were at a house in the 1400 block of West Lincoln Avenue and a small grass fire in the 1300 block of West Lincoln. On Sunday, a garage was destroyed in the 1400 block of Roosevelt Avenue. On Monday, two garages used as a family room were damaged in the 300 block of North Seventh Street.

At the Garfield scene, one of the occupants discovered the fire when he awoke to find flames coming in his bedroom window, according to the news release. Firefighters reported seeing heavy fire on the alley side when they arrived.

The injured firefighter caught himself on ceiling rafters as he fell. The residents were not hurt.

The fire did significant damage to the inside of the home; a fence was damaged and a vehicle destroyed.

The West Lincoln house fire caused only minor damage to the structure, officials said. Smoke flooded the interior through a crawl space, though.

The total damage amount for today’s house fires was estimated at $155,000.