Several other members of the security forces were slightly hurt as the aircraft plunged to the ground and caught fire, the Royal Ulster Constabulary said.
The badly hurt man was flown to Daisy Hill Hospital, Newry, for exploratory surgery on a severe chest injury. His condition last night was stable. The others were treated for minor injuries at the base.
Initial reports said a missile was fired over the perimeter fencing and exploded, destroying a helicopter. It was not immediately clear what height the aircraft was at when it was hit or what sort of missile was used. The RUC confirmed the attack came at about 8.30pm but said it could not give details.
Villagers said a big fire was followed by a series of bangs, thought to caused by the explosion of ammunition in the helicopter. Extra police and troops were drafted into the area and the village was sealed off in an effort to capture the attackers.
The Social Democratic and Labour Party councillor for the area, John Fee, said there was chaos at the scene. The attack was 'lunacy' and could have led to many civilian deaths.
The incident followed demonstrations yesterday when buses and vans were hijacked and set on fire in loyalist areas in north and west Belfast. Three people were arrested.
Security services have been on alert since terrorists attacked Heathrow airport 10 days ago.
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