Four Australian children — some as young as two months old — have been rescued from a global child exploitation ring following an international, multi-agency investigation.

Key points: A total of 16 people were charged with 738 child exploitation offences

A total of 16 people were charged with 738 child exploitation offences Interpol, Europol, US cyber and sex crime teams were involved in the operation

Interpol, Europol, US cyber and sex crime teams were involved in the operation The investigation began in 2018 when US detectives alerted Australian authorities

The two-year probe by the Australian Federal Police (AFP) and US Homeland Security targeted an online marketplace where users allegedly paid for child rape videos and images.

In total, 16 people were charged with 738 child exploitation offences and four children were rescued — three in NSW and one in Victoria.

The ABC understands the children were aged between two months and eight years old.

It is also understood at least three children were related to those alleged to have abused them, before images of the abuse were exchanged online through encrypted files.

"These crimes see people using significant established networks to share child abuse material and take advantage of vulnerable children," Victoria Police Detective Karen Bennett said.

"They have devastating impacts for victims and the wider community."

The investigation began in 2018 when US detectives alerted Australian authorities about a website where users paid for child abuse material.

A total of 18 search warrants were executed across Australia. ( Supplied )

Operation Walwa, as it was known, shared information with crime agencies including Interpol, Europol, US cyber and sex crime teams, as well as several Australian state and territory commands.

As a result, investigators executed 18 search warrants across NSW, South Australia, Queensland, Victoria and Western Australia.

Adam Parks from US Homeland Security said the arrests came at a "critical time".

"More so than ever, children are increasingly online for their schooling, to socialise with their friends and family, and to play games," Mr Parks said.

"Let this be a warning that law enforcement is undeterred by COVID-19 and remains on-duty to keep our children safe in Australia, the US, and online."

US detectives alerted Australian authorities about the abuse website in 2018. ( Supplied )

Former AFP officer and head of strategic policing at the Australian Strategic Policy Institute (ASPI), Dr John Coyne, said technology had "altered the way people access child exploitation material".

"Unfortunately, people are able to create global networks using off-the-shelf encryption and they can interact from their living rooms," he said.

These advancements have also enhanced the crime fighting capabilities of law enforcement, he said.

"We are seeing large-scale collaborations like this from across the world," Dr Coyne said.

"If you think you can sit at home and watch and not get caught; police will dismantle these groups and pursue users.

"These joint investigations should give the average mum and dad a sense of the scale and importance of tackling these crimes."