Two men have been arrested on suspicion of murder after the incident at an address in Tichborne Grove, which also left a 27-year-old woman with serious injuries.
A spokesperson for Hampshire Constabulary said: "We were called at 11pm last night to a report of a disturbance at an address in Tichborne Grove, Havant.
"On arrival, officers found a man and a woman who had both sustained stab wounds.
"Ambulance crews were in attendance but sadly the 21-year-old man from Havant, was pronounced dead at the scene. His next of kin have been informed and they are being supported by specialist officers."
The 27-year-old woman, from Southsea, was taken to Southampton General Hospital for treatment. Her injuries are described as serious but not life-threatening. police said.
Police confirmed a 25-year-old man from Cambourne, Cornwall and a 31-year-old man from Hayling Island have been arrested on suspicion of murder.
Both remain in police custody, police said.
Detective Inspector Lee McClellan from Hampshire Constabulary’s Major Crime Unit said: “We would like to reassure the public that we believe this to be an isolated incident and there is no wider risk to the community.
“We will be in the area throughout the day conducting our enquiries so if any residents have any concerns, please come and speak to our officers."
If you have any information that you think might help with our investigation, please get in touch by calling 101, quoting 44200184002.
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