An emergency operation is under way after 40 Army cadets, aged between 12 and 17, got into difficulties in the Mourne Mountains.
Coastguard, ambulance and helicopter crews have been called to the scene.
Medical staff are treating several of the children on the mountain. Weather conditions have been very poor.
The coastguard said it was understood that all members of the group are accounted for, however, four people may be suffering from exposure.
The Coastguard posted on Facebook that as many as 70 people may have got into difficulty.
It said the PSNI and ambulance service contacted the coastguard just before midday on Wednesday requesting assistance after receiving “several reports that a large number of people were in difficulty after being caught out in inclement weather”.
Three of its rescue helicopters and three teams went to the scene as well as the Mourne Mountain Rescue Team and police and the UK coastguard.
Colin McGrath, an SDLP MLA, tweeted: “Major emergency incident in the Mournes with helicopter, coastguard, medical and ambulance responding.
“Please God all will be ok.”
Police have advised motorists to avoid Head Road in Annalong due to a build-up of traffic. Drivers should seek an alternative route.