A 21-year-old woman who fell eight floors to her death from a hotel in Sydney's south had been arguing with her boyfriend, police say.

At 11.30pm (AEDT) on Wednesday paramedics were called to the Rydges Hotel in Cronulla after a report that a woman had fallen from a 10th floor balcony and landed on another balcony on the second floor.

The woman was taken to St George Hospital but she died from her injuries while undergoing emergency surgery just before 5am.

Police say alcohol may have also been a factor in the tragedy.

"One of the issues we will be looking at is the involvement of alcohol," Detective Superintendent Greg Antonjuk told reporters in southern Sydney.

"There are circumstances that indicate there was a disagreement between them, but there's nothing stronger than that at this point in time."

Police have since established a crime scene in the room in which the woman and her 27-year-old boyfriend were staying.

"The male has been spoken to, as have a number of people in the hotel," said Det Supt Antonjuk.

Police believe the couple had spent the whole day in Cronulla on holiday.

Detectives are in the process of talking to other hotel guests and witnesses who may have seen the couple at various venues during the day.

This included a restaurant where the couple dined just before returning to the hotel, police said.

"We have some queries at this stage, but they have to be tested against the evidence we're gathering," the officers said.

The family of the woman, originally from the South Coast, are now in Sydney.

Her boyfriend is also from the same area.

"He's obviously extremely distressed," said Det Supt Antonjuk.

"His family are also supporting him.