New laws designed to stop paedophiles convicted in Australia from travelling overseas to offend again came into effect Wednesday, with the government saying it will make vulnerable children safer.

It is now an offence for registered child sex offenders -- those convicted of the most serious forms of abuse -- to leave Australia without approval from law enforcement agencies.

They also face having their passports cancelled at the request of Australian authorities.

"Australia has up to 20,000 registered child sex offenders who have served their sentences but are subject to reporting obligations that help to protect the community," said Foreign Minister Julie Bishop.

"For too long, these predators have travelled overseas undetected, including to countries where weaker laws mean they have opportunities to commit heinous crimes."

Last year alone, 800 registered child sex offenders travelled overseas, often to developing countries in Asia, and about 40 percent did so without notifying police.

"This will now stop," said Bishop.

The move follows repeated episodes of child exploitation overseas, including a high-profile case last year when Australian Robert Ellis was convicted of sexually abusing 11 Indonesian girls on the resort island of Bali.

The crackdown comes on the heels of concern about the growing role of technology in paedophilia, with the government proposing new offences and tougher penalties targeting live-streamed child abuse and online grooming.

They also plan tougher fines on internet service providers if they do not report abusive material to police.

Justice Minister Michael Keenan called the crackdown "the toughest on paedophiles in a generation", making Australia "a world leader in protecting vulnerable children overseas from child sex tourism".