WATERVILLE — A Thursday night fire caused serious damage to an apartment building on High Street and injured at least one firefighter, but the cause of the blaze is still under investigation.

The fire was called in around 6 p.m. by a resident of one of the units at 11 High St.

Crews from Waterville, Winslow and Fairfield were at the scene, and the heat from the flames was apparently intense. One firefighter, Mike McKay, had to be taken out from the building and was later checked out by Delta Ambulance because of the heat, Waterville fire Chief David LaFountain said. Another unidentified Winslow firefighter was carried to an ambulance on a stretcher.

Daniella Chabot, who called in the fire, said she was outside smoking a cigarette when the fire began. As she was going back into the building, she said she could hear beeping. Then she said she saw smoke in the stairwell. She ran to get her son and dog, and ran back out of the building.

“I don’t know what caused it,” she said on the sidewalk across from the building, where thick, dark smoke had been billowing from near the roof of the brown house. She said the building had propane and old wiring, which could have been the cause.

LaFountain said he did not know the cause of the fire, and it was being investigated by Capt. John Gromek. LaFountain said given how hot the fire was in the building, it was possible the building would be gutted. He did not know if anyone had been inside at the time of the fire.

One tenant, who only identified himself as Pete, said he still had a cat inside at the time of the fire. He lived on the first floor and said he had no idea what caused the fire. Pete, who said he had been a firefighter for six years, was yelling for the firefighters to get moving early on at the scene.

As dozens of spectators stood watching the flames and smoke, the water was eventually turned on around 6:15 p.m., and heavily sprayed in the building. A ladder truck brought firefighters to the upper levels of the building to break windows, spray water in and chainsaw holes into the building.

Gromek said the investigation would take a while. He said apparently no one was home in the third-floor unit at the time.

The Red Cross issued a news released Thursday night saying the organization’s Disaster Action Team was offering emergency aid to the three families that were affected by the fire.

Colin Ellis — 861-9253

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Twitter: @colinoellis