Police are investigating a fatal collision on the A470 near Storey Arms in Powys, mid-Wales, which left four people – including two women and two men – dead.
The accident occurred between Libanus and RAC bends at around 11.15pm on Friday. It involved two Volkswagen cars.
Dyfed-Powys police have said the road was closed overnight but reopened in the morning.
Five teenage males were believed to have been travelling in convoy and were arrested on suspicion of dangerous driving. A police statement said that three passengers involved in the tragedy were taken to the hospital and are in a serious condition.
A police statement said that three passengers involved in the tragedy were taken to the hospital and are in a serious condition.
Both of the deceased men are from Barry, Vale of Glamorgan. Their next of kin have been informed.
Superintendent Chris Curtis said: "This is a tragic incident and our thoughts are with the families at this difficult time. We are working with South Wales Police in order to provide support to the families affected and also the communities they live within.
"We will work with partners to ensure that the incident is fully investigated," he added.
Dr Dylan Jones, headteacher of Ysgol Gyfun Bro Morgannwg, Barry, confirmed that one of those killed was a sixth-form pupil at the comprehensive school, and a former student at the institution had also died. One of those seriously injured is also a pupil at the school.
One of those seriously injured is also a pupil at the school.
"We had a junior [assembly] this morning and some of the sixth form were stewarding the event when news started to come in," said Jones.
"I have spoken to both parents and we are preparing for Monday so that we can offer all assistance and counselling to the pupils."
Officers are urging anyone with information to get in touch with the Dyfed Powys Roads Policing Unit by dialing 101.