The platoon chief of the Saint John fire department says emergency crews were called to the six-unit townhouse at around 10 p.m. on Friday after the carbon monoxide detector went off.
Steve Voutour says the property’s lease owner and her mother heard the alarm, and without a key to the building, forced their way inside.
Voutour says three people were sent to a local hospital in critical condition and two of them were later moved to a hospital in Halifax.
He says two residents of an adjacent unit were taken to a Saint John hospital for evaluation and later released.
Voutour says a natural gas fire burner was found inside the building and the cause of the leak is being investigated.