A multi-agency investigation is under way into an incident which resulted in the death of a 60-year-old man in Newcastle, Co Down, on Friday night.
The man has been named locally as William Stockdale.
The Northern Ireland Fire and Rescue Service (NIFRS) was called to the property at an address at Castlewellan Road where high levels of carbon monoxide were detected.
Five people, including two paramedics responding to the call, were treated for the effects of carbon monoxide poisoning. All five were later released from the Ulster Hospital in Dundonald.
Carbon monoxide is a colourless, odourless, and poisonous gas that can accumulate in the home as a result of faulty appliances or poor air circulation.
"The death of a 60-year-old man in a house on the Castlewellan Road in Newcastle is a tragedy," said local Sinn Féin representative Chris Hazzard.
“It has shocked and saddened the local community.
“I want to express my condolences to the family and friends of this man at this difficult time,” he added.