Disturbing footage has emerged of a group of teenagers allegedly assaulting a tourist before throwing his phone in the ocean at a popular holiday spot in Melbourne.

Victoria Police say a 34-year-old Norwegian man was visiting St Kilda Pier on Thursday when he was approached by the group at around lunchtime.

The group allegedly bashed the man, stole his phone and then threw it in the ocean. 

Police say the group are aged between their late teens to early 20s.

Footage posted on social media shows the terrifying moment the man was chased by the group, before they allegedly assaulted him in front of bystanders. 

The man was taken to hospital and treated for a broken arm.

He was planning to stay in Australia for Christmas but has now returned to Norway. 

Police were called to the scene, however the group had already fled by the time officers arrived. 

Investigators have released images of three men and a woman they believe can assist with their enquiries.

One of the men is described as being in his early 20s, of Mediterranean/Middle Eastern appearance, with a thin build, short goatee beard and black curly hair.

The second man is described as being in his early 20s, of Caucasian appearance, short goatee beard and short brown hair, and was wearing a black New York Yankees beanie and open grey short sleeve shirt at the time.

The third man is described as being in his late teens to early 20s, of Caucasian appearance, with curly hair with shaved sides and was wearing a Chicago Bulls #13 jersey and carrying a black satchel bag.

The woman police wish to speak to was seen wearing a red bikini. She has a number of distinctive tattoos on her chest, leg and arm and is described as being in her early 20s, with a slim build and dark hair.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000.