WORCESTER — Alan ­Thorpe was asleep in his recreational vehicle in the backyard of his home on Larch Street Tuesday, when his dog’s incessant barking woke him up.

Thorpe’s chocolate Labrador retriever was one of several neighborhood dogs sounding the alarm for an early morning fire of suspicious origin that ­destroyed two buildings and damaged several others.

When Thorpe looked up, all he saw was flames.

“Hey, the whole neighborhood is on fire,” Thorpe told State Police, who answered his 911 call. He rushed through the three-family building he owns on Larch Street, making sure his parents, sister, and son got out of the building.

“The fire just jumped from building to building. I watched. The fire started there,” he said, pointing to the vacant three-family building on Merrick Street.

About three-quarters of the city’s firefighting force responded to the blaze, according to Deputy Fire Chief Geoffrey Gardell.

One witness said the sky was aglow from burning embers.

“When I woke up, I saw something blow up like a bomb or something,” said Joao Leite, a second-floor tenant of a nearby building on Merrick Street.

Three firefighters suffered minor injuries, according to Gardell, and one of the residents of the affected houses suffered burns to his back and head. He said he was treated at the scene.

Gardell said 20 people from several buildings were displaced by the fire.

He said that the fire may have been set and that officials were looking for a person of interest.

Fire investigators, aided by an excavator, began going through the charred remains Tuesday morning after the blaze, trying to find the origin and cause of the primary fire.