3.45pm UPDATE: Video - two men seriously hurt in Southsea 'public order' incident
Police said paramedics are in Alhambra Road after the incident at 12.45pm today.
The road is shut from Mansion Road to Granada Road.
Police have set up a cordon and forensics officers can be seen dusting down two bikes and putting down evidence markers.
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Hide AdA Hampshire police spokeswoman said: 'Four black men fled the scene, heading in the direction of Palmerston Road.
'Enquiries to establish the circumstances of the incident are ongoing. We are unable to confirm any further details at this time.
'Anyone with information is asked to call 101.'
A spokesman for South Central Ambulance Service said: ‘We were called at 12.39pm to reports of two males in their 20s who had suffered serious injuries following an assault.
‘We sent a rapid response vehicle, two ambulances, one of our senior officers and the air ambulance also landed nearby.
‘Both patients were taken to Queen Alexandra Hospital by road following treatment at the scene.’