The emergency services were tasked to Levaghery Gardens in Portadown.
The PSNI says it is investigating the circumstances surrounding “the sudden death” of a man in his eighties at the house.
A police spokesperson said last night: "A post mortem will be carried out in due course. A woman also believed to be in her eighties has been taken to hospital for treatment.”
It is still unknown why a Hazardous Area Response Team officer was tasked with two rapid response paramedics, two ambulance crews as well as the charity Air Ambulance with a helicopter emergency medical services (HEMS) crew on board.
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A Northern Ireland Ambulance Service spokesman said it was called to the Levaghery Gardens area of Portadown at 4.53pm on Wednesday after reports of a male unconscious.
One elderly female patient was taken to Craigavon Area Hospital.
A spokeswoman for the Southern Trust said the woman remains in a stable condition in hospital this morning.
UUP MLA Doug Beattie expressed his sadness at the news.
"Sad news coming from Levaghery Gardens, Portadown," he said. "My thoughts are with the family and friends at this difficult time."
DUP councillor Margaret Tinsley also voiced sadness at the news.
"My thoughts and prayers are with this family, just devastating for them."