Police have cordoned off an area of woodland off Aldermoor Road, opposite Aldermoor Avenue, after a woman reported she was assaulted there shortly before 8.30am this morning.
The victim was jogging through the wooded area when she was assaulted by a man who then ran off.
The man is described as in his late 20s around 5ft 10 inches tall and slim. He was wearing a black rain coat.
Anyone with information is asked to contact the Western Area CID team at Southampton Central police station on 101 or call Crimestoppers anonymously on 0800 555 111.
More top news
Wednesday's weather for the east of the region
Wednesday's weather for the west of the region
Britain falls silent to remember the July 7 attacks amid a welter of warnings about the enduring threat from terrorism a decade on.