Four men believed to visiting Melbourne from interstate for a buck's party are being questioned by homicide detectives after a woman's body was found in their hotel room.

Emergency services were called to Oaks on Market in Melbourne's CBD about 8am Sunday, where the woman's fully clothed body was found in the shower.

She is yet to be identified but is believed to be aged in her 20s.

She was found wearing a black, long-sleeved top, blue denim shorts and white running shoes.

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Her death is being treated as suspicious.

Homicide detectives have taken four men into custody for questioning.

All aged in the late 20s and early 30s and from the ACT and NSW.

A crime scene has been established at the hotel, where forensic police have spent the day gathering evidence.

Police are waiting on the outcome of an autopsy.

Charges have not been laid.

The Herald-Sun reported there were 11 men at the buck's party in the two bedroom apartment on level 10 of the Market St building.

One of them phoned emergency services after finding the woman unconscious in the shower.

While four have been detained, the remainder of the group have returned interstate.

Fairfax Media reported the group rented three rooms at the hotel and went to the football, before heading to King Street nightclub Cloud 9.

Members of the group declined to tell reporters who the dead woman was or how they met her.

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