Three people were injured and taken to hospital on Thursday following a gas explosion at a house under construction in Fort Saskatchewan.

The explosion happened near 140 Allard Way in the Southpointe neighbourhood around 1:15 p.m.

Fire officials have determined that the incident was caused by a gas explosion in the basement of the house. The explosion and subsequent fire were quickly contained by fire crews.

Roman Michalycia told CBC News that his nephew and two sons were inside at the time.

Michalycia said his sons walked out of the the house. But his nephew was in more serious condition and had to be airlifted to the University of Alberta Hospital where his sons are also receiving treatment.

"They're shaken up," Michalycia said. "My nephew, they're not sure. They're more concerned about him."

Dean Vanderwolf was working nearby at the time of the blast.

"When I turned around I saw the remainder of the flames coming out," he said. "And when I got down, it was just smoke and a little bit of flames and guys are running around."

A ladder was used to get the workers out of the basement.

"Their clothes were burned off ... right to their skin," Vanderwolf said. "Their hair, their face was burned."

All three men are in serious condition.

Alberta Occupational Health and Safety is now investigating.