An 11-year-old boy is accused of setting a fire that tore through the roof of a new emergency room still under construction at Winnipeg's Grace Hospital.

Crews were called to the construction site, on the north side of the hospital, around 10:50 p.m. Monday.

Fire officials said the water supply was restricted because one fire hydrant wasn't working. However, they contained the flames mostly to the roof.

The boy was arrested in connection with the fire but he is under 12 and therefore too young to face charges under Canadian law, police said.

Rob Kerr, who lives near the hospital, noticed the fire from his home and called 911.

Grace Hospital emergency dept. Fire on new construction site. <a href="https://twitter.com/ctvwinnipeg">@ctvwinnipeg</a> <a href="https://twitter.com/hashtag/Winnipeg?src=hash">#Winnipeg</a> <a href="https://t.co/Y6PCaOqxGB">pic.twitter.com/Y6PCaOqxGB</a> —@Robert_Kerr

"I looked at the window and I could see this bright orange glow coming just through the crack in the blinds. I looked out and there was just large flames shooting up right at the last section of the new construction that's going up," he said, adding the response from emergency crews was quick.

"There were trucks everywhere within a matter of, probably, three or four minutes."

They couldn't get to the flames right away, though, because of the construction fencing around the site, Kerr said. They cut away a section to climb through and dragged a hose closer to the building, he said.

There was no fire or smoke damage to the rest of the hospital and no one was hurt, fire officials said.

Booth Drive was closed for about 1½ hours before reopening around midnight.