Thirty one children, some as young as two, have now been rescued from a massive global child sex ring on the dark net with a New Zealand man at the centre.

US Homeland Security contacted New Zealand Police's Online Child Exploitation unit (OCEANZ) on September 8, 2015 with concerns about a Canterbury link to the offending.

Detective Senior Sergeant John Michael, the national manager for OCEANZ, told the Herald how the arrest of Christchurch man Drew Webb, with the help of Canterbury's Child Protection Team, opened up a new phase of the global investigation.

"This group, many of them parents or step-parents of children, were part of this group focused on the sexual exploitation of their own children," he said.

Webb, who was jailed last year, was facilitating the group and importing and distributing images and film of children being abused, included toddlers and babies.

"Once that offender was arrested that opened up a whole new phase of investigation where we identified, around the world, people that we believed posed a really high risk to their own children," Michael said.

The ring had spread to several countries including Australia, US, Canada, Scotland and France.

Eighteen people have since been arrested and four convicted for child exploitation and child sex offences.

Today, Scottish paedophile Hugh Sim was jailed for eight years at the Glasgow High Court for filming himself abusing a three-year-old, BBC reported.

His arrest came after New Zealand Police shared information with their Scottish counterparts and within 20 minutes of receiving the tip-off Scottish police were knocking down Sim's door.

Scottish High Court Judge Johanna Johnston said Sim's images were distributed online and found by police in New Zealand.

"Had it not been for the work of the police in this country and the authorities in New Zealand your offences may never have come to light," BBC reported the judge saying.

Scottish police Detective Superintendent Andy Lawson said it was "without doubt one of the best examples of law enforcement working at an international level that I have ever witnessed".

"More crucially the prompt and professional actions by all of the officers concerned in this case enabled a child, indeed potentially other children, to be protected from further harm by this perpetrator."

Michael said the victimisation of the children will continue for the rest of their lives.

"Unfortunately I don't know how many children will identify as being victims, but that number I would suggest will grow as time goes on," he said.

He couldn't comment further on any other New Zealand links to the group due to ongoing investigations.

"That is possible," he said of possible Kiwi offenders. "We're always looking."

Michael said in many cases child sex offenders will identify a network where "others of their kind will operate".

"They'll look at working in the dark net where they have a level of anonymity. It's not difficult to find like-minded individuals unfortunately," he added.

​He said the nature of the crime, a level of anonymity, and "the fact that it's done from the privacy of their own home" makes it hard for authorites to track offenders.

Some offenders globally have already received sentences of more than 20 years' prison, with one US-based offender jailed for 30 years.

In February, US woman Ashleigh Welsh was jailed for 27 years for recording child sex videos at her home near San Antonio, Texas and sharing them with the online group, the San Antonio Express-News reported.

And in 2016 US man Jason Janatsch pleaded guilty to producing child pornography.

Janatsch's offending was linked to Webb in Christchurch, according to US Department of Justice records.

"Janatsch, using his iPhone, transmitted the photographs to the New Zealand man. According to court records, he also received child pornography from the New Zealand man in return," a Department of Justice statement read.

New Zealand Police Commissioner Mike Bush said in his latest blog that he was "extremely proud of the work done on this case" by New Zealand police.

-NZ Herald