The small, green structure had been home to a number of businesses in the past, including a used car dealership and a golf driving range, but police said it had been vacant for a number of years, and the windows and doors were boarded-up after some vandalism last summer.
Greg Aitken, who lives across the street, was awakened by his wife around 5:30 a.m. after she saw flames coming from the back of the structure.
He said the flames were just in one corner, but spread quickly.
"Within five to ten minutes about half the building was engulfed," he said.
Another neighbour, Reggie Jameson, said he woke up after hearing sirens and looked out his window to find the vacant building was on fire.
"Just one corner of the building, you could see a little bit of flames," said Jameson in a phone interview from his home on Saturday. "Within two to five minutes the whole building was engulfed.
"It just kept getting worse and worse as more fire engines showed up."
The Charlottetown Police Service said an officer on patrol in the area came across the fire and an injured male.
Deputy Chief Gary McGuigan said the man told the officer that there could be more people inside the building.
"The officer went to the building and attempted to enter but was pushed back by the intense heat and smoke," said McGuigan.
The injured male was airlifted to a hospital in Halifax.
McGuigan said after the fire was extinguished roughly two hours later, the three bodies were found inside.
Jameson, 24, said he could see flames shooting out of the building from every direction.
He said when he learned that three people died in the fire, it came as a shock because the building is abandoned and was boarded up.
"There's no power hook ups to it, there's nothing. There's three feet of snow in front of it," said Jameson, who has lived near the building for about two years. "It never occurred to me that anyone was inside."
But Jameson said he has occasionally seen flashlights and heard people talking inside the building late at night, but usually only during the summer.
Aitken said he hadn't seen any tracks in the snow around the building and was surprised to learn anyone was inside.
There had been graffiti painted in three sides of the building. Aitken said it had been there since last summer.
The building is located behind the busy Charlottetown Mall, and McGuigan said there is a lot of young pedestrian traffic in the area.
The fire completely gutted the single-storey structure and part of the roof near the rear of the building had collapsed.
Police said investigators were working to identify the victims and determine the cause of the fire.
McGuigan said he knew there was much discussion on social media about the possible identities of the victims and injured male, but said police would not confirm any names until after autopsies to be performed in Charlottetown on Sunday.
He did say it was believed that all the victims were young.
As of Saturday evening, McGuigan said police had not been able to speak with the injured male, but hoped to get a statement from him soon.
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