Officers were called to a house with three apartments on Brussels Street around 1:45 a.m. after a wooden third-storey deck suddenly collapsed onto a second-storey deck, Sgt. Nancy Rudback said.
Rudback said several people were on the top deck at the time and there were also several people on the bottom deck.
"There was a social event at the residence, a party, and there were people on both decks," she said.
Investigators said six people — four women and two men in their early 20s — were taken to hospital.
Five were taken from the scene by ambulance with serious injuries and one went to hospital a few hours later, said Rudback.
Rudback said most of the injured people were on the bottom deck at the time of the collapse.
On Saturday afternoon, the third-story deck stood upright on its side in the driveway next to the home. It appeared the deck was only attached to the home at one side.
The fencing on the lower deck was damaged, but otherwise appeared intact.
There were remnants of a party strewn around the yard. A keg sat on its side on the driveway, surrounded by red plastic cups.
A few young men who said they lived in the residence declined to comment, but said they were shaken up.
Rudback said the home's owner is being interviewed and a city building inspector will investigate.
"We would be dealing with criminal negligence if that's what the (inspector) found, but we're so early in looking at it that it would be hard to say which course it will take at this point," she said.
Last September, about 15 people were injured after a deck collapsed in the neighbourhood of Dartmouth.
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