A 47-year-old man faces 145 charges of rape, child exploitation and grooming offences allegedly committed in three Australian states.
The charges include five counts of rape, four of indecent treatment of children and eight of grooming children to engage in sexual acts, police said.
The man, from Warwick in south-east Queensland, allegedly committed the offences between 2002 and 2015.
Police have identified 28 alleged child victims so far, a statement said.
The victims were identified in Queensland, New South Wales and Victoria. The police statement said more victims could be found as far away as Western Australia.
Police say the man, who cannot be named for legal reasons, targeted children on a variety of social media sites, using names including “Jazz”, “Jazzman” and “David Bourne”.
“In some cases it will be alleged victims met the man and were subsequently taken to a hotel room where offences were committed,” the Queensland Police statement said.
The operation was a joint investigation between the Warwick Child Protection and Investigation Unit and detectives from Taskforce Argos, the Queensland Police Service specialist online child exploitation team.
Taskforce Argos had earlier said it was thwarting at least one online sex predator targeting children each week.
‘Shock and relief’
The case comes as Australian Federal Police (AFP) in Canberra are working with Dutch police to examine a hard drive containing “many thousands” of child sex abuse images, allegedly taken by an Australian man arrested last month in the Philippines.
The AFP told the BBC that 256 Australian registered sex offenders had travelled to the Philippines in the past four years.
Police have been working on the Warwick case since April last year, trying to identify all the victims, said Detective Senior Constable Russell Joyce.
“The reactions when we have found them have been everything from embarrassment to shock and in some respects, relief,” he told the Warwick Daily News.
“We are still going and we believe there are more victims out there,” he said.
The case was briefly heard in the Warwick Magistrates Court on Monday.