The attack happened on Sunday in a room on the seventh floor of the Cumberland Hotel.
Yesterday, officers arrested three men aged 56, 34 and 32 on suspicion of attempted murder following raids at addresses in north London, according to a Scotland Yard statement.
A 31-year-old woman was also arrested on suspicion of handling stolen goods. All four remained in custody today, police said.
One of the victims remains in a critical condition in hospital. The other two women are also in hospital, but their injuries are not believed to be life-threatening, the statement said.
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No keys were stolen from the hotel and police said there had been no breach of security at the venue.
Detectives are scouring security camera footage to establish the movements of both the women and the suspects earlier on Saturday.