Police are worried by a spike in underage prostitution in Auckland's CBD, with girls as young as 12 selling themselves for sex.

Senior Constable Mark Riddell of the Auckland central police Youth Action Team said in the last six weeks, a police operation code-named City Door had identified at least 13 girls aged under 16 who were "active prostitutes".

Many of them work from City Road, which runs between Queen Street and Symonds Street. Senior Constable Riddell calls the street a "young red light area".

In the last two weeks, Senior Constable Riddell and his team have taken five underage girls off the streets and put them in to the custody of Child, Youth and Family. But Riddell said many of these girls escape CYF and go straight back on the street.

"Kids will run away on the same night we pick them up," he said. "On some occasions, they've got back to the city before we've got back out on the road."

One of the girls, who started working as a prostitute when she was 12 and had never been to high school, said she had been picked up by a car full of men and raped only days earlier.

Police placed the girl in the care of CYF, but Senior Constable Riddell said she ran away soon after.

He said CYF has only about 100 beds in secure custody across New Zealand. These are prioritised for those at risk of suicide, so the girls he dealt with often missed out.

Debbie Baker, the manager of Streetreach, a group supporting street sex workers, said she knew of at least 12 girls between 11 and 15 "out there selling themselves for sex" in the central city.

"Young meat earns a lot of money," said Ms Baker. "Underage prostitution has always been a problem, but there is an increase. We're seeing more and more young girls out there."

Ms Baker said she knew of a 12-year-old West Auckland girl who was recruited by a gang outside her school to sell cannabis.

After spending the drug money, the girl was forced into prostitution to pay her debt to the gang and she shared the extra earnings from her work with her family.

"Her parents knew exactly what she was doing."

Ms Baker said she believed the police were under-resourced and CYF was unable to deal with the problem.

"These girls may be abused in their home and all the police have got the power to do is to take them back there. The police really do have their hands tied.

"We need to protect our children - and these are children, regardless of where they've come from. Child prostitution is child abuse and it needs to be given the same penalties. It needs to be given the same priority as child abuse."

Senior Constable Riddell also believed many of the girls' parents knew what they are doing.

"They're just happy a few dollars come in each week, because a lot of them will spread the money to family," he said.

Auckland Mayor John Banks said he was concerned by what he calls an epidemic of prostitution, family violence and drug and alcohol abuse in greater Auckland.

"We'll never be a Super City as long as we've got kids as young as 12 on the streets selling themselves for sex," said Mr Banks.

"I'm calling for the setting up of a new multi-agency taskforce to fight illicit drugs, alcohol abuse, violence, crime and prostitution... all of these agencies are talking at each other, not with each other."

Minister of Youth Affairs Paula Bennett supported Mr Banks' suggestion but said there was no easy answer to the problem.

"We are confronted with a community issue where men are paying for sex with underage women," said Ms Bennett. "Clearly, no community wants that for their young women and Auckland is no exception.

"So I am delighted Mayor John Banks is taking leadership on this issue, I welcome any ideas from the local council and I would certainly support a co-operative effort between agencies."

CYF northern regional manager Marion Heeney confirmed the increase in underage prostitution and said she was also aware of 13 underage girls working as prostitutes in Auckland CBD .

"It is unclear what the reason for the apparent upsurge is or whether it signals a trend, but it is obviously concerning," said Ms Heeney.

Senior Constable Riddell believed the increase in underage prostitution in the CBD may be a result of police efforts to clean up "young red light areas" in South Auckland, such as Hunters Corner in Papatoetoe and spots in Manurewa, forcing the girls into the city.

"I would say there's probably not a problem out at Hunters Corner at the moment," said Ms Baker. "The girls travel, they have access to cars and friends with cars. They go to places we might not even know of yet".

Senior Constable Riddell said many of the girls used P, and has found girls as young as 13 staying with adult drug dealers.

Ms Baker said she wasn't surprised many of the girls used drugs, but they were not the only issue.

"For some of them, they can be out there for a packet of smokes or survival or because they're actually being abused at home, so they'd rather get paid for it," she said.

"I've had girls say to me: 'Deb, I can't do this straight'. Some of the things the girls have to do are pretty horrific so no wonder they take drugs."

Annah Pickering, the New Zealand Prostitutes Collective Auckland regional manager, said while she didn't dispute the increase, neither she nor her staff had come across child prostitution in Auckland central recently.

"Our organisation is out there regularly and I haven't come across any 12-year-olds for a long time," said Pickering, who added NZPC staff were "not out there 24/7".

Pickering said adult sex workers discouraged children from working as prostitutes because it was "not good for business".

While Operation City Door has had some success, Senior Constable Riddell said his unit's next step would be getting Auckland City Council, the Langham Hotel and other stakeholders involved by providing better street lighting and car park security on City Road.

He said the Langham Hotel's car park attracted "undesirables".

"We want to make the area less user-friendly for them."

In a statement, Langham managing director Jeffrey van Vorsselen said the hotel was unaware of the situation.

"However, it is pleasing that the Auckland Police are taking a proactive response to this issue allegedly occurring in the area," said Mr van Vorsselen. "As a responsible business, we will support any initiatives to improve our local community."

Mr Banks said he would do anything the police wanted to make City Road safe.

"If the police came to me about street lighting, I'll put in more lighting on City Road."