Police were tasked in the early hours of this morning, Thursday 26th October, to the Ballykeel II area of Ballymena, after receiving a report of an unresponsive male.
It is understood Northern Ireland Ambulance Service also dispatched two emergency crews to the scene at a block of flats in Orkney Drive.
The man, aged in his 30's, was taken to hospital where he remains in a serious condition.
Police have maintained a presence at the flats throughout Thursday morning.
Commenting on the incident, a spokesperson for the Police Service of Northern Ireland said:
"Police in Ballymena received a report of an unresponsive male in the Orkney Drive area, in the early hours of today, Thursday 26th October.
"The report was received shortly before 5am, that a man, aged in his 30’s, had been found unresponsive inside a property and had to be taken to hospital by ambulance staff.
"He currently remains in hospital in a serious condition."