Emergency services were called to the incident in Llanberis, Gwynedd, close to the Snowdon Valley Mountain railway line, at 08:30 BST on Sunday.
North Wales Police said a "multi-agency response" is under way. Police, Llanberis Mountain Rescue, North Wales Fire and Rescue Service and the ambulance service are all at the scene.
The incident is currently ongoing.
Two people have died following an incident in a north Wales village, BBC Wales understands.