Hawke's Bay police say there has been a "quite alarming" increase in pre-teens posting and exchanging nude pictures of themselves online.

Children were unknowingly and unwittingly feeding into the hands of predators, Detective Sergeant Heath Jones said.

Jones said in one case in Hawke's Bay recently an 8-year-old with unrestricted access to the internet posted nude pictures of themselves and uploaded them to YouTube.

The video was immediately taken down and their parents were mortified, but the child had no real understanding of the consequences, he said.

"While it is a global trend, in Hawke's Bay we have noticed that it is not teenagers, but pre-teens who are exchanging and posting sexualised pictures of themselves.

"They are being given devices at an earlier age, and they have easy access to the internet.

"We have noticed an increase in the number of pre-teens in Hawke's Bay doing this and we need parents to be aware."

Jones said the most vulnerable population, and years were Year 7, 8, 9 and 10.

"Incidents seem to drop off at Year 11."

Youths - both boys and girls - typically exchanged pictures with fellow peers, he said.

"A large group are sending them to peers, but some are using chat rooms to exchange these pictures.

"In chat rooms, typically, they don't have to form a relationship or know the person. And that's what is worrying because a predator could pretend to be a young person and children would exchange pictures willingly."

He says the pictures being exchanged are essentially "child porn" and they come under the category of objectionable material.

"There has been an increase in the amount of times we are investigating people in possession of objectionable material, and essentially what these kids are doing is child porn.

"My biggest concern is these young kids willingly send images out there.

"They are willingly, and conscientiously feeding [predators]. It's quite alarming to me that it's happening in Hawke's Bay."

Jones said some children had easy access to hardcore porn and it was "warping their view of what is normal".

"We have found that a lot of the intermediate school age groups look at hardcore porn which has abuse and objectifying of women, and they see that as normal.

"Parents need to acknowledge that easy online access to pornography is a major problem affecting our children.

"These children they don't understand the consequences and the fact that an image lasts forever.

"Parents need to be on top of this, because social media outlets are not doing enough."

He encouraged parents to use the NetSafe and ConnectSmart websites, but said the need to keep an eye on a child's use of social media and devices was greater than ever.

"Parents need to have regular conversations about the dangers of internet and sharing.

"With older kids they need to pick their battles - establish devise-free zones. With the younger kids start teaching them young about safe use."

He also advised parents to look at other sites like thelightproject.co.nz which helps people navigate the changing pornography landscape and how to deal with it.