Officers and medics were called to Pickwick House in Wingfield Street, Buckland, after the 26-year-old man was attacked at around 12.43pm today.
Police arrested a 23-year-old man on suspicion of murder and said they are ‘not currently seeking any other suspects’. He is in custody.
Detective Inspector Matt Gillooly 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.
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‘We will be in the area conducting our enquiries so if any residents have any concerns, please come and speak to our officers.’
Members of the public rushed to give aid to the victim.
Shaun Truman, 34, said he saw the man stagger and collapse.
Mr Truman said: ‘I was walking down the alley between Ark Dickens School and the block of flats next to it and a guy came running past me at full speed, which I thought was odd.
‘Then I heard people shouting from Pickwick House balconies saying “help him” and “he’s been stabbed”.
‘When I looked back down that’s when I saw the injured man staggering towards me, heavily bleeding from his face and chest and struggling for breath and he collapsed on the floor.’
He called an ambulance and was relaying instructions to put pressure on the wound – thought to be in the chest area – to another man helping.
Mr Truman added: ‘He was breathing, we put pressure on the wound to ease bleeding and got him into recovery position as advised by the call handler but help was there almost instantly.’
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One resident said he and his family were shocked and scared by the incident.
Mohammed Sadik, 39, who lives in Wingfield Street, said: ‘We just came out, I’m really shocked and it’s really stressful.
‘There’s so many police officers and ambulance and different police wearing protective vests.
‘I’ve been living here for five or six years and it’s the first time we’ve seen that outside our building.
‘This is all scary and I’m in absolute disbelief.’
South Central Ambulance Service sent the South East Coast Air Ambulance Helicopter, which landed at Buckland park, and the Hampshire & Isle of Wight Air Ambulance critical care car.
The victim died was pronounced dead outside Pickwick House.
Anyone with information should call police on 101 quoting 44210011248.
Alternatively, call the crime-fighting charity Crimestoppers anonymously on 0800 555 111.