James Callaghan Drive has been closed between Fort Southwick and the top of Southwick Hill Road after the two-car crash earlier at about 2.15pm today.
A Hampshire Fire and Rescue spokesperson said two men were injured, and one had to be removed from his car by firefighters.
The road remains closed while police deal with the aftermath of the incident.
QA Hospital has asked people travelling to and from the hospital to use an alternative route.
A post on Facebook said: ‘Staff can still access Fort Southwick and the car parks onsite there but Park and Ride services for staff will be delayed.
‘The Park and Ride is currently only stopping at the bus stop outside the main entrance of QA.
‘The bus stop outside North entrance is currently not being used. We apologise for any inconvenience.’
The road is expected to be closed until about 6pm.