Officers attended the High Street around midday following the collision, involving a white Nissan van.
Despite best efforts, the pedestrian, an 85-year-old woman from Portsmouth, has been pronounced dead.
Her family are being supported by officers.
The van driver, a 61-year-old man from Cosham, has been arrested on suspicion of causing death by careless driving.
Officers investigating the exact circumstances of the collision are keen to speak with any witnesses or anyone who has dash cam footage.
If you can assist, please call 101, quoting the reference number 802 of today’s date (October 7).
The road was closed while officers attended, but this has now been reopened.
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