A woman was sexually assaulted twice by the same man in Norwich city centre early on Saturday morning, a police spokesman said.
The attacks happened between 0515 and 0545 BST and the first was close to Magdalen Street flyover.
Later the woman was assaulted again, this time in the Elm Hill area.
The suspect is described as between 18 and 25 years old, of Mediterranean appearance, about 5ft 7in (1.7m) tall, slim with short dark hair.
He was wearing a black leather jacket, dark jeans with black and white trainers.
Police have appealed for witnesses or anyone with information to contact them.