Cesar Oviedo was taking out the trash at an apartment building on Greenville Street in Roxbury on Thursday when he heard a crackling noise and smelled smoke.

“Oh, the boat’s on fire!’ he recalled thinking.

A 30-foot boat next to the apartment building had ignited, heavily damaging a house on its other side, which was under construction, and sending smoke into the occupied apartments.

“I rang the fire alarm and I got everybody out the building,’’ said Oviedo, who is a maintenance worker.

The cause of the three-alarm blaze is still under investigation, but fire officials said at the scene that it started in the boat at around 11:45 a.m.

It quickly spread to the home that was under construction, where no one was living at the time, Deputy Fire Chief Andre Stallworth said. The fire was put out by 12:30 p.m.

The residents of the apartment building huddled outside, awaiting notification that it was OK for them to go back inside. Several people credited Oviedo for getting them out safely.

“He was the one running around and saying, ‘Everybody get out the house,’ knocking on doors,’’ said Maritza Morales, who has lived in the apartment with her children for four years.

No one was injured and it is likely that no one will be displaced, Stallworth said.

“They checked the buildings quickly,’’ Stallworth said.

“We were concerned that somebody might be sleeping in the boat. We did a primary search there,’’ he said.

The fire caused up to $700,000 in damage to the empty home, and $50,000 in minor burn damage to the side of the apartment building where Oviedo was working. The right side of the empty house appeared heavily charred Thursday, while investigators inspected the burned boat, named “Kelly.’’

Homes and apartment buildings tightly lined the Roxbury street where the fire occurred.

Stallworth said he was worried because the neighborhood is a compact one. “We didn’t want it to take off,’’ he said. “Fortunately it’s not a windy day.’’

“Once you get a building, two buildings going on, that radiant heat can feed on itself,’’ Stallworth said. “And that’s why we like to strike alarms to get ahead of these things.’’

The fire was especially frightening for Morales, who was still shaking while standing on the street.

Her daughter usually sleeps on the side of the apartment building that was burned, she said, but she was at school at the time.

“It was crazy. . . . We didn’t know what was going on,’’ she said.

“Then I went back in the house to get some pants, because I had shorts on.’’

J.D. Capelouto can be reached at jd.capelouto@globe.com. Follow him on Twitter @jdcapelouto.