A man in his 30s was flown to hospital and three men have been arrested after an attack in Northampton town centre, police have now confirmed.
Eye-witnesses told the Chronicle & Echo the man was attacked while walking with friends.
There are no confirmed details as to the nature of the injuries but East Midlands Ambulance Service praised police for "controlling blood loss" of the victim before medics arrived.
A spokesman for Northamptonshire Police said: "Police were called to an incident in St Katherine’s Gardens, St Katherine’s Street, Northampton, at about 6.30pm yesterday (Tuesday, August 7) following reports of an assault. The victim, a man in his 30s, was taken to hospital by air ambulance where he is currently being treated.
“Three males were arrested in connection with the incident and are currently in police custody.
“An investigation is underway and witnesses or anyone with any information should call Northamptonshire Police on 101 or Crimestoppers anonymously on 0800 555111, quoting incident number 417 of 7/8/18.”
Sol Central was closed to the public following the incident and several roads around Horsemarket and College Street were also taped off.
The eyewitness, who wanted to remain anonymous, saw the air ambulance "hovering really low near the bus station" and said there were PCSOs on bikes.
"It looked like they were looking for somebody," the eyewitness said.
"I got past the Park Inn next to the Spring Boroughs area and I saw ambulances and police up near Sol Central, and I saw it was all cordoned off."
East Midlands Ambulance Service Ambulance Operations Manager John Coyles said: “We received a call to College Street, Northampton, shortly after 6.30pm to a man who had received serious injuries. Police were already on the scene and deserve great praise for controlling blood loss until we arrived.
“We sent an ambulance and paramedic car and the patient was stabilised before being taken to hospital,by Derbyshire, Leicestershire and Rutland Air Ambulance."