A woman is recovering in hospital after being followed into a lift and repeatedly stabbed in the chest and stomach.
Police said they were called at 3pm on Thursday afternoon after the woman, who is 41, was found with stab wounds.
She was attacked in a block of flats in Hoxton, in East London.
It is not known if the woman knew her attacker and police are now investigating.
Detective Sergeant Barry Hart said: "We have established that the woman was stabbed in the lift of a block of flats by a male suspect.
"It is possible that this male suspect has been hanging around the block – Wimbourne Court, off Wimbourne Street and Shaftesbury Street in Hoxton – both immediately before and in the days leading up to the stabbing.
"We need to hear from anyone who has seen a suspicious male in and around Wimbourne Court, as well as anyone with information that may assist the investigation."
Anyone with information is asked to call detectives at Hackney CID on 020 7275 3410 or via 101 or quoting reference 4533/ 19 April.