A 15-year-old boy has died and a 14-year-old girl is in a critical condition after falling into a quarry.
The incident took place near Limekiln Road in Abersychan, Torfaen, on Wednesday evening.
Gwent Police said the boy, from Pontypool, died at the scene.
A Coastguard helicopter was needed to rescue the girl, from Blaenavon, from the quarry and she is now being treated at University Hospital of Wales in Cardiff.
One councillor said the incident would have reverberations throughout local communities.
The Welsh Ambulance Service said it received a 999 call at 18:30 BST, while South Wales Fire and Rescue Service said it sent two crews to the scene.
HM Coastguard said the Welsh Ambulance Service asked for assistance at 19:20 due to the nature of the terrain at the quarry.
A spokeswoman added that the coastguard helicopter was sent from its base in St Athan and the paramedic was winched down to rescue one of the casualties.
She was then flown to a Cardiff heliport before being taken by ambulance to the University Hospital of Wales.
Torfaen council said it was working closely with the leadership team at the boy's school to provide support for everyone affected.
"Our colleagues from the educational psychology service have been at the school since the start of the day and further support is also on hand from the school counselling service," it added.
It added that the land is privately owned.
The Reverend John Edward Funnell, from Noddfa Church in Abersychan, said he was "so proud" of how the valley has come together.
"Last night messages were off the hook as we saw helicopters flying through the valley. We were all deeply concerned about what had happened," he said.
"This morning the community has rallied together, it's been wonderful to support each other," he added.
"The local school has been fantastic, and the emergency services have been brilliant. I'm so proud of how our valley has come together in this time."
Councillor Janet Jones, who represents Blaenavon, said: "This is a tragic incident, and the effects of it will have reverberations throughout the communities of Blaenavon and Abersychan.
"My thoughts are with the two families, and I'm sure the local community and the local community council will rally around to support them through this terrible time."