About 250 Australians with child sex convictions have travelled to the Philippines in the last four years, the Australian Federal Police (AFP) has revealed.

Filipino police are currently pursuing a case against Australian man Peter Gerard Scully for what they allege are some of the worst child sex offences in the nation's history.

The AFP was involved in the investigation and arrest and says 250 known Australian child sex offenders travelled to the Philippines in the past four years.

A spokesman has told the ABC that Australia alerts Filipino authorities when a sex offender boards a flight, but it is up to them whether to refuse entry.

Scully, 51, who has no previous convictions for child sex abuse, was arrested and charged with sexually abusing 11 children aged between 18 months and 13 years.

He allegedly spent years sexually abusing and torturing young children and streaming his crimes online, where the AFP says he charged between $US100 and $US10,000 for the videos he filmed.

The Melbourne man has also been charged with the murder of one of his alleged victims, a 12-year-old girl, along with rape, torture, human trafficking and violating cyber laws.

On Saturday, authorities in the Philippines said Scully was working with foreign accomplices in his child pornography operation and launched a manhunt for four foreigners believed to be involved.

The Australian embassy held an emergency meeting late last week in relation to the case.

Editor's note 13/4/2015: An earlier version of this story said 250 Australian sex offenders had travelled to the Philippines in the last year.