New Zealanders are watching a concerning amount of pornography featuring fantasies about step siblings or step parents, the Chief Censor says.

And while extreme or highly aggressive porn is not particularly popular in this country, there was also a worrying level of non-consensual behaviour in New Zealanders' favourite porn videos.

The findings were based on the 200 most popular videos watched by Kiwis on website Pornhub in the last year, which were analysed by the Classifications Office.

Chief Censor David Shanks said the most surprising finding was that nearly half of the most popular videos had narratives involving sex between blended family members.

"This was not something that was evident in earlier content research, particularly pre-internet research," he said at a press conference in Wellington today.

"That was surprising and a little bit shocking."

This trend was not limited to New Zealand, as "step porn" had become a major theme in pornography around the world.

Mature viewers would realise that these scenarios were fake and contrived, but the fantasy aspect of the videos might be less clear to teens who were still forming their views on sex, Shanks said.

Many of the narratives involved a family member who was reluctant to engage in sex but went through with it under pressure. This could "reinforce some stereotypes around no becoming yes".

Extreme content was not particularly popular among New Zealanders, the analysis found.

One of the 200 videos featured choking during sex, and around 13 per cent of the videos featured throat-holding which did not cut off breathing.

Around 10 per cent featured physical aggression like pinching, slapping, hair-pulling, or evidence of unhappiness.

A quarter of the videos featured affection, such as kissing, embracing or soft touching. And just 3 per cent featured condom use.

"It is clear from this latest work that porn provides a very poor model for young people who are developing their understanding of consent and of what a healthy sexual relationship looks like," Shanks said.

"They need a real counterpoint to the fictional and confusing stories that porn offers.

"Now it is more important than ever to give our young people the information and education they need in this space."

The Classifications Office released a study of teens' porn viewing habits last year, which showed that porn was "a fact of life" for many young New Zealanders.

Many of them used porn to learn about sex, and expressed concern about how it could impact their sexual expectations or behaviour.

"The reality is young people are seeing porn and it's time to start talking to them about that," Shanks said.

The Government is preparing law changes to regulate online pornography.

Internal Affairs Minister Tracey Martin has said she hopes to introduce the proposals to Parliament before the next election.

"A number of different approaches are required – some practical, some education and possibly some involving regulations. This includes preventing children and young people from accidentally being exposed to pornography and from deliberately accessing it in a digital environment, including at school."

The Government law changes were influenced by reforms in the United Kingdom, which have now been shelved.

Britain's Conservative Government decided not to bring into force a 2017 law that would have required internet service providers to install porn-blocking software with all new internet connections, forcing subscribers to "opt out" of the porn block rather than actively "opting in" to it.

The British law would also have required anyone trying to access any of about 500,000 known porn sites to provide proof, such as driver's licences or credit cards, to verify that they are not under age.

THE FINDINGS
• 196 videos and 46 hours of data analysed from website Pornhub
• 3% showed condom use
• 46% were about step/family fantasies
• 10% showed physical aggression
• 29% showed some form of affection
• 35% contained non-consensual behaviour