AN AUSTRALIAN teacher is accused of luring beggar children as young as five from the Phnom Penh riverfront to his rented apartment, where they have told police they were sexually abused.

In the northern Philippines, a Victorian man allegedly filmed himself sexually abusing children and then uploaded the videos to the internet.

Increasing numbers of Australians are being apprehended in South-East Asia's poorest countries on child-sex charges amid growing concerns over a billion-dollar cybersex industry targeting impoverished children, including toddlers.

The children are being forced to perform sex acts that are streamed online to pedophiles around the world, investigators say.

Two Australian men have recently been jailed for paying children from the Philippines to perform sex acts live streamed to their Melbourne homes.

Before being jailed for 11 years in a Melbourne court in July, 68-year-old Patrick Ronald Goggins told police his victims as young as five would be ''out on the scrapheap, living on rubbish'' if he did not pay them to perform.

In one of the latest cases to emerge overseas, Australian Federal Police tipped off Cambodian authorities to the alleged activities of Australian teacher George Moussallie, 52, who has been charged with sexually abusing three boys aged between five and 11.

''He has known the boys at the riverside for a long time, since around 2010. The boys are very poor and are beggars on the riverside,'' said Sieng Sok, a Phnom Penh court deputy prosecutor.

Mr Sieng Sok said Mr Moussallie, who taught English at the private American Pacific School in Phnom Penh, admitted taking photographs of naked children but denied the children's claims of sexual abuse.

Police have seized a laptop computer, about 20 memory cards and three USB sticks from the apartment of Mr Moussallie, who was taken into custody last Thursday.

Police have not linked him to any cybersex operation.

In another new case, authorities in the northern Philippines raided a 65-year-old Australian man's home and found him uploading videos of children to a pornographic website linked to an illegal cybersex operation, the ABC reports.

The man, whose name has not been released, has been arrested along with his partner as well as the mother of three children who were allegedly being abused.

Officials said the man had been living in the Philippines since 2011.

Philippine regional director of the National Bureau of Investigation said the videos were being sold to computer users.

Fairfax Media has previously revealed that two other Australians, Hilton Reece Munro, a former Melbourne private school teacher, and Peter James Robinson, an engineer, are facing child sex charges on the Philippine resort island of Cebu, a cybersex hotspot.

The men deny any wrongdoing.

Authorities in Cebu have vowed to stamp out the abuse of children after the discovery of several operations where the sexual abuse of children was streamed to pedophiles in Western countries, including Australia.

The Philippine National Police's anti-cybercrime unit says that online pornography is now the number one crime in the Philippines.

Victorian Country Court judge Elizabeth Gaynor last month found that truck driver Brett Geoffrey Le Gassick, 43, had engaged in the ''wholesale exploitation of desperate children'' before sentencing him to 11 years' jail for remotely abusing more than 50 young Philippine girls.

Specific Commonwealth charges were introduced in 2010 to target Australians involved in the sexual abuse of children overseas, either in person or via the internet.

The offences carry penalties up to 20 years in prison.