The UK public broadcaster BBC led international condemnation.
In a statement, the BBC said: "This police raid against our partners at ABC is an attack on press freedom which we at the BBC find deeply troubling.
"At a time when the media is becoming less free across the world, it is highly worrying if a public broadcaster is being targeted for doing its job of reporting in the public interest."
The BBC's head of newsgathering Jonathan Munro said the raids were "deeply troubling" and were "completely contrary to free media".
The police action made headlines around the world with the New York Times noting that "no other developed democracy holds as tight to its secrets".
"The raids are just the latest example of how the country's conservative government will go to scare officials and reporters into submission."
The power of the police to search through thousands of emails of journalists in search of sources shocked CNN's chief media reporter Brian Stelter.
"We almost never see this in a democratic country like Australia," he said. "Something very troubling (is) happening on multiple fronts in Australia."
Reporters Without Borders said the images of AFP officers entering the ABC headquarters in Sydney on Wednesday was more like a scene from an authoritarian country, rather than a democracy.
“Persecuting a media outlet in this way because of a report that was clearly in the public interest is intolerable,” said Daniel Bastard, the head of RSF’s Asia-Pacific desk.
“This kind of intimidation of reporters and their sources can have devastating consequences for journalistic freedom and independent news reporting.”
ABC Managing Director David Anderson said he was heartened by the international coverage and support from colleagues across the globe.
"I had an email come in overnight from the director-general of the BBC offering his personal support," he told ABC radio on Thursday.
"This has got the world's attention as to how important it is that we are able to go about our journalism."