Underground ravers poisoned by carbon monoxide in Norway

More than 20 people have been hospitalised in Norway after they were poisoned by carbon monoxide at an underground rave.

The party took place in the national capital Oslo on Saturday night, the BBC reported.

Police were investigating a group of young people spotted acting in a confused fashion, when another person came out of the underground bunker and asked for medical help.

A total of 25 people were treated in hospital, among them two police officers who helped the victims.

All 25 are now recovering and out of danger.

There were about 200 people at the rave. Authorities are urging the others to monitor themselves for signs of carbon monoxide poisoning - such as nausea, headaches and dizziness.

It's believed the source of the poisoning were portable generators used at the rave, with other attendees complaining of overall poor air quality.

Serious carbon monoxide poisoning can lead to brain damage or even death.