Armed police officers were called to Deansgate in Manchester after the woman was attacked inside the venue.
Witnesses described seeing a woman “moaning” and in “severe pain”, lying on the ground in a car park.
The victim, who flagged down officers at 11.10am, is being treated in hospital for lacerations to her neck, Greater Manchester Police said.
Four men were arrested – two 26-year-olds, one aged 20 and one 24.
Police also detained a 20-year-old woman and a 17-year-old girl.
In some reports, a woman is pictured being led out of the hotel wearing jeans, a white vest top and gold flip flops, while the other is described as being in “silky pink pyjamas”.
A room is taped off inside the hotel and an area is cordoned off outside.
Greater Manchester Police said the incident is not believed to be terror related or a “random attack”.
Anthony Hilton, 32, who works at a letting agents close to the hotel, said: “One of our colleagues walked past and saw a lady on the floor with what appeared to be her throat slit.”
She was “well-dressed” and appeared to be in her 30s, he said.
“There must have been 15 undercover and normal police cars out in the street. Police were running to and fro from the car park and the Hilton Hotel,” he added.
Officers were seen speaking to guests and staff inside the 47-storey Beetham Tower, where the hotel is based.
Anyone with information should call 101, quoting reference number 726 of 23/07/2018. Alternatively, they can call Crimestoppers, anonymously, on 0800 555 111.