Specialist scene of crime officers are making a detailed search of a Stamshaw street after what is believed to be a stabbing at around 2pm this afternoon.
The incident has seen Strode Road by The Willows, close to Twyford Avenue, cordoned-off for most of the afternoon as police scour the area.
Armed officers and police dogs are still in attendance whilst the NPAS police helicopter searched overhead.
It is understood from Police sources that man in possession of a firearm at the scene are unconfirmed at this time.
Detectives are asking people to avoid the area as the investigation progresses. Anyone with any information or who was at the scene at the time is asked to call Portsmouth police on 101. Alternatively you can call the Crimestoppers charity anonymously on 0800 555 111.