"Unfortunately a fight broke out between two groups on the bus." Police used capsicum spray to break up the fight and disperse the roughly 30 youths who boarded the bus. Some were then taken to Chelsea police station so care could be provided to minimise the effects of the capsicum spray, with an ambulance attending as a precaution. Video shows the youths being hosed down with water by police. Chelsea beach is a target of police's "Operation Summersafe". Credit:Nine News. About 20 youths boarded trains to leave the area.

No one was injured in the incident. An 18-year-old man was arrested but later released. Police are investigating whether he was involved in several incidents that occurred on Wednesday night. "Unfortunately the hot weather brings bad behaviour in some," Ms O'Grady said. This month, police launched Operation Summersafe, which aims to discourage bad behaviour along Port Philip Bay beaches over the summer period with increased police presence. Deputy Commissioner Shane Patton said the response to Wednesday's incident showed police were prepared for unruly behaviour.

Loading "Our operation worked the way it should have, and moved it away [from the beach] before the offending occurred," he said. Mr Patton assured local businesses that police would continue to deal with the threat, and advised them against taking the law into their own hands. A Chelsea resident, whose home overlooks the beach, said locals were fearful of going to the beach on hot days when they expected bad behaviour. "It happens every hot day. It will probably happen again tomorrow," he said.

"I'm going to stay indoors on hot days – you don't feel safe on those days anymore. In the afternoon when people have been drinking all day on the beach, towards the end of the day, that's when the trouble happens." The resident, who did not want to be named, said he believed most of the youths who misbehaved came from the outer south-eastern suburbs. "They come to Chelsea because it's the closest beach to them with the amenities open at night time that they're after – supermarkets and bottle shops and food," he said. Police last year had to step up patrols following a spate of violent incidents at Chelsea beach. A man was glassed in the face with a beer bottle and other bathers had their possessions stolen as they swam, in a crime spree police described as "deeply disturbing". On Wednesday, Superintendent Sharon McKinnon said Operation Summersafe would have a particular focus on beaches where previous incidents involving misbehaving youths had occurred, including at Chelsea and Mordialloc.