An investigation has been launched and scene is likely to remain throughout the day.
Lindsay Road remains sealed off with cordon tape since early Sunday morning with an officer in a garden. A number of other surrounding roads have been cordoned off, Lindsay Road, Ellwood Avenue and the flats on Solent Ave, that goes down as far as Marston Road.
Officers are likely to remain in the area and will do for the foreseeable future, said the spokesman.
Police are expected to release details shortly and thanked the public for their co-operation and patience.
Claims have been made that a stabbing took place in the property and the person has suffered life changing injuries.
Joanne Harrison said, I was shocked when I opened the curtains this morning not seen this before.
“On arrival, officers found a 17 year-old boy with a stab wound. He is currently being treated in Southampton General Hospital and is in a serious condition.