Emergency services rushed to the scene just after midday, at the junction of St George’s Road and Eastney Esplanade.
Two vehicles were involved in the crash, and footage show police and other personnel on the road.
Hampshire police are clearing the road, and investigating what happened.
A spokeswoman from Hampshire Constabulary said: ‘We were called at 12.12pm today to a report of a road traffic collision involving two cars on Eastney Esplanade.
‘No serious injuries have been reported at the current time.
‘We are at the scene and the road is currently closed.
‘We would urge road users to avoid the area and take alternative routes while the road is being cleared.’
Fire crews from Cosham and Southsea provided emergency care to one person who escaped the vehicle, and a nearby pedestrian.
A spokesman from Hampshire and Isle of Wight Fire and Rescue said: ‘Crews from Cosham and Southsea were called to Eastney Esplanade, Southsea, at 12.12pm following a road traffic collision involving one car on its roof.
‘No one was trapped. Firefighters provided immediate emergency care to one person who had got themselves out of the vehicle and one pedestrian who had fallen nearby.
‘Crews left after handing the incident over to police.’
Firefighters left the scene at 1.11pm.
Portsmouth Roads reported that both lanes on Eastney Esplanade were closed by emergency services.
‘RTI Eastney Esplanade opposite Coffee Cup - Emergency services in attendance, both lanes closed’, Portsmouth Roads reports.