ILLEGAL and dangerous bush raves are putting partygoers and emergency workers at serious risk, police have warned.

A growing number of dance parties have been held in reserves across the lower north shore over the past 18 months, often during the full moon and often in dangerous locations.

Police say up to 200 people were turning up the events, receiving invites and details via text message.

media_camera This cliff at Chowder Bay is one of many in reserves across the lower north shore. Picture: David Swift

Partygoers have been seen swimming naked beside cliffs at Middle Head in one rave and another was in asbestos-filled tunnels at Chowder Bay.Police said hundreds of people turned up to the most recent rave at Balls Head last month.

The party was shut down by police and the organiser was fined $500.

media_camera Historic fortifications at Middle Head in Sydney Harbour close to where people were seen swimming naked.

Constable Johnson, of North Sydney Police, and a colleague, who helped stop a party in a bunker and tunnels at Chowder Bay in June last year, said the events were putting police at risk.

“In the tunnels we don’t know what we are walking into,” he said.

The party was carefully organised as it had both a generator and DJ equipment hired from a business in the city.

There were allegedly drug-affected and drunk people aged from 16 to 20 at the party and risks included nearby cliffs, wildlife and tree stumps. The organiser was fined $300.

Chowder Bay, Sydney NSW

Senior Constable Tim Young of North Sydney Police, said people could be killed or severely injured if they fell down one of the cliffs at the reserves.

“They are putting people’s lives in danger as well as emergency services,” ­Constable Young said.

media_camera Police are concerned about a bushfire being sparked by cigarettes or generators at the raves. This photo is of a managed burn at Balls Head. Picture: Braden Fastier

A National Parks and Wildlife Services spokesman said rave parties had become a problem at a number of locations.

During the party at Chowder Bay “considerable damage was caused to the heritage site”.

“A lot of rubbish was left behind and graffiti and asbestos disturbed after people broke in to one of the locked tunnels using an angle grinder,” he said.