The failure to stop incident took place on the the junction of New Road East and New Road today around 6.55pm Sunday 11th April
Police are keen to speak with anyone who witnessed the incident or may have captured the incident on CCTV or Dashcam.
Shocked residents claimed the man was riding his pushbike when he was struck by a black coloured vehicle that failed to stop.
Officers from Hampshire Police Roads Policing and Paramedics from South central ambulance rushed to the scene. Paramedics treated the male for a head injury before he was transported to the QA in Portsmouth.
The vehicle that made off has been described as a black Skoda Octavia, which may have been a taxi or private hire vehicle.
Police specialists are searching for clues on the road that remains closed for collision investigation work.
CCTV that captured the collision has also been reviewed by Police.
Anyone with information that may assist officers is asked to call 101.