Police in Auckland are hunting for a serial sex attacker they believe is as young as 12.

At least 11 women have reported being indecently assaulted while out running or walking alone in the Onehunga area since last October.

Two of the assaults happened within three hours of each other in February, with the most recent attack on Gambia Avenue on Easter Sunday.

In each case, the victim was approached from behind and indecently assaulted.

Photo: NZ POLICE

Police describe the attacker as aged between 12 and 16, Māori or Pacific Islander, of thin to slim build, with light brown hair possibly dyed a yellow/brassy colour.

In many cases he had been wearing a grey hooded sweatshirt and knee-length shorts.

The primary location of the offending appeared to be in the area around Fergusson Domain, but other assaults had occurred in Oranga Avenue, Arthur Street, Grey Street and Amaru Street, police said.

Photo: RNZ / Daniel Walker

Speaking from Fergusson Domain, Detective Constable Patrick Whitiora said such behaviour would not be tolerated.

"This young man may have told someone about what he's been doing.

"He needs help, he needs to be stopped.

"Please, if you suspect that it may be your mate, your brother, your son - you can help us."

Photo: RNZ / Carla Penman

Three incidents took place over three days between 2 February and 4 February this year. Two of them occurred within the space of three hours on the morning of 13 February.

Police have made door to door inquiries at more than 100 homes and more than 700 flyers have been hand-delivered to houses in the area.

"The description of this offender is of a very young person," Mr Whitiora said.

"Behaviour such as this in a young person is worrying, and we want to not only apprehend this person to obviously stop any more indecent assaults but we also need to get him help."

Residents worried

Jax Clarke, who works close to Fergusson Domain, told RNZ she would be taking precautions after hearing about the attacks.

"I've had some real reassurance from the community constable in terms of just doing the right things to be safe," Ms Clarke said.

"But I certainly wouldn't walk through here if I didn't know I was going to someone who was expecting me very shortly, or if I didn't see other people around," she said.

Another local resident, Ally Barton, who lives around the corner from the domain, said it was scary that some of the women had been attacked in broad daylight.

Auckland Council, meanwhile, said there were no CCTV cameras installed at the domain or in the surrounding streets.

Police are asking anyone who recognises the young man to call 0800 748 244.