Four people have been arrested on suspicion of murder after a 20-year-old man was killed in what police believe was a stabbing.
Officers from Sussex Police were called by paramedics to an address in Spencers Road in Crawley during the early hours of Saturday morning.
Police said the man, from Mayfield in Crawley, who has not been named, was treated for what was believed to be a stab wound to the abdomen and died a short time later in hospital.
Two women, aged 24 and 22, and two 20-year-old men, all from Crawley, were arrested.
Detective Chief Inspector Antony Archibald from Sussex and Surrey Police said: "This has been a fast moving investigation and we are still making enquiries. We have arrested four people who are being questioned.
"A scene guard has been set up in Spencers Road and there are officers in the area to speak to residents about their concerns."
Witnesses are asked to call Sussex Police on 101 or Crimestoppers anonymously on 0800 555 111.