A man was stabbed in his left forearm and chest, and left seriously injured, at about 7.30am yesterday.
The 34-year-old man was attacked by a man with whom he was visiting a house in Whitefriars Road, Hastings.
After the knife stabbing, the victim ran out of the house and is believed to have been pursued by his attacker.
Police say he was "bleeding profusely" from his arm wound and also had a puncture wound to the side of his chest.
In the space of about seven minutes, he ran along Whitefriars Road, Emmanuel Road and into Vicarage Road, where he knocked on a door and asked for help.
An ambulance was called.
Now Sussex Police is seeking witnesses.
Detective Constable David Elcock said: "While the assault took place in the house in Whitefriars Road, we would like to hear from anyone who saw the victim between the time he left the house around 7.30am and 7.37am when the alarm was raised.
"The suspect is known to the victim and we are looking for him at this time."
If you saw either of the men or have any other information, email firstname.lastname@example.org or call 101 quoting serial 239 of 31/07.
Alternatively, you can call the independent charity Crimestoppers anonymously on 0800 555 111.