More than 20 people have been taken to hospital with carbon monoxide poisoning after attending a rave in an underground bunker in the Norwegian capital, Oslo.
Police say the party was discovered by chance when a patrol came across a group of young people acting confused early on Sunday.
Several more then emerged from a bunker and asked for an ambulance.
Authorities believe the poisoning was caused by portable generators.
Two of the 25 victims are thought to be police officers who tended to the partygoers.
“Fortunately, they are all improving. We can say that they are out of danger,” chief physician Fridtjof Heyerdahl at Oslo University Hospital told Aftenposten newspaper.
Around 200 people are thought to have attended the rave, according to Oslo police.
Police also called for other attendees to seek medical attention if they started suffering from nausea, headaches or dizziness.
One person who left before police arrived told public broadcaster NRK he had exited the rave for fresh air on numerous occasions because of the poor air quality inside.
Oslo police say they are investigating why a tip-off about the rave was not acted upon.