Andrew Colvin of the Australian Federal Police said the victims were 'disturbingly young'
Australian police have charged at least 19 men with being part of a global child pornography network involving people in 70 countries.
The investigation was prompted by a tip-off from Brazilian police.
The men who have been charged include a police officer, a senior lawyer and a childcare worker.
Some 500,000 images of child abuse and 15,000 videos were seized, and the Australian Federal Police said more arrests were expected later this week.
Some of the seized videos showed victims as young as 12 months old, while others showed children being abused for more than two hours.
"These are some of the worst images, I must say, that the Federal Police have ever seen," Australian Federal Police Deputy Commissioner Andrew Colvin told reporters.
The Australians said that information supplied by Brazil to the international policing network, Interpol, had helped identify more than 200 suspects in 70 countries.
At least two children had been removed from harm as a result of the investigation, police said.
Although it is difficult to identify the victims of abuse, they appear to be based primarily in Eastern Europe, and North and South America, according to the BBC correspondent in Sydney, Nick Bryant.
All the charges relate to accessing the images over the internet, using what is called a peer-to-peer network.
The method allows members to share files without going through a central network server, avoiding filters operated by internet service providers, making the crime harder to detect.
But Australian Federal Police Assistant Commissioner Neil Gaughan said law enforcement officers did have ways "we can get in and infiltrate these type of applications".
The charged men each face a 10-year sentence for possessing child abuse material.