Twenty-five people have been taken to hospital with carbon monoxide poisoning after attending an illegal rave in a bunker in the Norwegian capital, Oslo.
Five are in a critical condition and two police officers who tended to the partygoers are among those poisoned.
Authorities believe the poisoning was caused by portable generators.
Police say the “Rave Cave” event, attended by some 200 people, was discovered by chance when a patrol met a group of confused young people.
Several more then emerged from the bunker and asked for an ambulance.
It was not immediately known who had organised the underground event which was reportedly planned three weeks in advance and kept secret from the authorities.
Oslo police say they are investigating why a tip-off about the rave was not acted upon.