Officers were called at 01:50hrs on Sunday, 6 April, to the Cumberland Hotel in W1 following reports of an assault.
At this stage, it is believed that a single male suspect entered a guest bedroom on the seventh floor of the building, where three women and three children were sleeping in adjoining rooms.
Detectives believe that the suspect was disturbed when some of the occupants of the room woke up, and the three women were subsequently assaulted with a hammer which was later recovered at the scene.
The victims are all UAE nationals aged in their 30s, and all sustained head and facial injuries.
'Victim One' is in a critical but stable condition at a central London hospital. 'Victim Two' and 'Victim Three' both sustained serious injuries but their conditions are not life-threatening.
At this stage, officers retain an open mind regarding the motive for the attack.
The investigation into the incident is being led by detectives from the Homicide and Major Crime Command, under Detective Chief Inspector Andy Chalmers.
DCI Chalmers said: "This was an unusually violent attack on three women and I am very keen to speak with anyone who was in or around the hotel between 01.00hrs and 02.00hrs on Sunday morning.
"Did you see or hear anything that could be of use to my officers? If so, we would like to hear from you as soon as possible."
The incident room can be contacted on 020 8358 0100.
