At least 27 revellers have been hospitalised with carbon monoxide poisoning after they were sickened during an illegal rave inside an underground bunker.
Five people were in a critical condition and two police officers who helped the revellers were among those who were poisoned at the "Rave Cave" event in Oslo, Norway.
The carbon monoxide level in parts of the bunker was "many times" more than the lethal level, and the oxygen level was barely 16%, below the minimum safe concentration of 19.5%, said officials.
Investigators have blamed fumes from portable diesel generators, which were used to power the sound system and lights in the venue which is about 230ft (70 metres) underground.
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