A serviced apartment where a woman was found dead on Sunday morning is believed to have been rented out for a buck's party.

Police were called after the body was found on the 10th floor of the Oaks on Market building, between Collins Street and Flinders Lane, about 8am.

The circumstances surrounding the death are unknown.

People at the building said the room was being rented out by a buck's party group from Canberra.

It's believed the woman returned to the hotel room with the men on Saturday night.

One of the men woke to find the woman dead in the shower, The Age has been told.

Four men, aged in their 20s and 30s, are in police custody.

The dead woman is yet to be formally identified. She is believed to be aged in her mid to late 20s.

A concerned hotel guest called emergency services, police say.

A group of women who stayed at the hotel overnight said they didn't hear anything unusual aside from sirens just before 8am.

Homicide detectives carrying evidence bags were seen leaving the building about 1pm.

Detective Nick Densley said an autopsy would be performed "as soon as possible".

Police refused to comment further until the woman was identified.

Anyone with information can contact Crime Stoppers on 1800 333 000.