A 21 year old woman is in Wellington Hospital with serious bruising and swelling to the head, following an unprovoked and vicious assault in the early hours of this morning.

Detective Sergeant Penny Gifford of the Wellington City CIB says the victim was walking home from the San Francisco Bath House around 1am this morning, making her way to Wallace Street, Mount Cook.

"As the victim walked along Wallace Street around 1:30am, she was approached from behind by an unknown male and punched to the ground. She was then punched repeatedly to the head before residents were alerted to her screams. At that point, the offender ran off towards John Street."

The offender is described as a Caucasian, in his mid to late twenties, with short, possibly blonde hair. He was wearing a pale blue and white bomber style jacket.

Penny Gifford says, "We are urging anyone who may know this offender to come forward as soon as possible. We're also keen to speak to a woman also walking south along Wallace Street at the time, a taxi driver who pulled up in the area about 1:30am and a male in the area who spoke to residents after the attack."

Anyone with any information should contact the Wellington CIB on (04) 381 2000 or phone Crimestoppers on 0800 555 111.