UXBRIDGE — The fire moved swiftly through the converted two-story farmhouse Monday night, quickly consuming the ground floor apartment where a single mother and her 6-year-old daughter lived, witnesses said.

Tenants of the five-unit, wood-frame building called out for the mother and daughter. But there was no answer.

On Tuesday morning, firefighters found the girl’s body under smoldering debris. Hours later they found her mother, Suzanne Donovan, 45. Officials did not release the victims’ names, but Donovan’s identity was confirmed by friends.

Nine people lived at 629 East Hartford Ave., and seven were accounted for by early Tuesday. There had been little hope that Donovan and her daughter were not inside, as neighbors said it would have been unlikely for her to be out late on a school night.

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“The smoke, you couldn’t go under it,” said Justin Hutchinson, who lived above the victims. “The smoke was completely black — the heat, it was crazy.”

Throughout the morning, neighbors in this sparsely settled community dropped by the scene and expressed sorrow for the two lives cut short. And at Donovan’s workplace, co-workers mourned.

“She was such a fabulous person. She brought laughter into this place every single day,” said Melissa Ringer, a salon coordinator at the Sherborn Day Spa, where Donovan had been manager for about six months.

“This is truly a tragedy. Everyone here is so sad,” Ringer said in a telephone interview. She said Donovan occasionally brought her daughter into the spa and that the girl had an infectious smile.

Robert Ouellette, who has lived in the apartment building for two years, said the pair were homebodies. Donovan was considered a doting mother to her daughter, who started first grade in the town’s elementary school this month.

The fire broke out around 10:30 p.m. and firefighters had difficulty getting water to the scene. The nearest hydrant was about 1,200 feet away, and firefighters were forced to link pump trucks together by long lines of several connected fire hoses to reach the hydrant, said Uxbridge Fire Chief William Kessler. It was unclear Tuesday if that played a role in the fatalities. Several water tanker trucks were brought in, and firefighters from at least 14 surrounding communities helped battle the three-alarm fire.

Authorities have not determined the cause of the fire or where it started. A source with knowledge of the investigation said the two bodies were not found together, suggesting that perhaps the two victims were either immediately overcome or lost each other amid the chaos.

Justin Hutchinson, whose apartment was directly above Donovan’s, said he arrived home Monday night and noticed that smoke was rising along his apartment’s walls.

Hutchinson said he ran downstairs and saw Donovan’s living room engulfed in flames. He and a friend ran around the back of the apartment and kicked in the door, he said. They tried to enter the house but thick, black smoke choked them.

They then broke the bedroom window, Hutchinson recounted, but voracious flames shot out.

“There was nothing I could do,” Hutchinson said.

“The smoke, you couldn’t go under it. The smoke was completely black — the heat, it was crazy. The whole house just caught up in it, in maybe a matter of 10 minutes.”

Chris Evans, who helped alert tenants about the fire, said it took just minutes for the floor of the building to collapse.

Ouellette said someone shouted “Get out!’’ to alert him of the fire. He grabbed his cat, ran outside, got into his car, and drove across the street and discovered that the front of the building was engulfed.

As he and other residents gathered, they quickly realized that Donovan and her daughter were missing. They alerted arriving emergency personnel about the possibility they had not made it out, he said.

He said the fire is devastating to everyone who lived in the L-shaped building, a reality that hit residents as they watched firefighters try to put out the massive fire.

“A couple of tenants were screaming and crying. Everything we owned was going up in smoke,’’ Ouellette said.

Jeffrey May, a pastor who lives across the street from the building, saw the flames.

“I looked out the window and saw flickering in the distance. I grabbed my flashlight and ran to the woods because I wasn’t sure if it was our property on fire,” he said. “I wasn’t sure if it was a forest fire, and then, of course, I saw the house burning.”

May said the residents who made it to safety kept talking about the missing mother and daughter.

“We were hoping and praying that they were gone someplace or that some family members took them away for the weekend, but it just doesn’t work that way,’’ he said. “It’s just awful.”