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

The apartment was being rented out by 11 men, in town from Canberra for a buck's party.

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, Fairfax Media has been told.

Four men, aged in their 20s and 30s, were released from police custody late Sunday night, pending further enquiries. The men are from the ACT and New South Wales, police say.

The dead woman is yet to be formally identified.

She is believed to be aged in her 20s and was wearing a black long-sleeved top, blue denim shorts and white runners.

The circumstances surrounding the death are unknown.

Police are testing for the presence of illicit drugs. Their findings will not be available until Monday or Tuesday. 

Two of the men at the buck's party said they went to a football match, then returned to their rented hotel rooms before heading out to King Street venue Cloud 9.

Some of the men were seen downstairs at the club between 2.30am and 3am.

One of the men said the group had rented three hotel rooms for the night.

They would not say who the deceased woman was or how they met her. 

They told Fairfax Media they had been "stitched up".

Seven of the men, who have been described as witnesses to the incident, left the hotel about 2.30pm.

The groom-to-be remained inside the hotel lobby, talking on his mobile phone. 

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.

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.

theage.com.au