A convicted child molester was prevented from flying overseas from Sydney airport on Wednesday under new laws aimed at keeping Australian paedophiles from traveling to south-east Asia for sex tourism.

Laws that took effect on Wednesday prevent 20,000 convicted paedophiles listed on the Australian child sex offender register from leaving the country except for specific purposes approved by law enforcement agencies.

Australian paedophiles are notorious for taking inexpensive holidays to nearby south-east Asian and Pacific island countries to abuse children.

The Australian foreign affairs minister, Julie Bishop, would not say where the paedophile stopped in Sydney was headed. He was being questioned by police.

It is now a federal crime punishable by up to five years in prison for registered child molesters to leave the country without law enforcement agencies’ permission.

About 320 convicted sex offenders left Australia last year without registering their plans with government authorities.

“We are aware they have a high propensity to reoffend if they are in a country where they are not monitored and where child sex exploitation is rampant,” Bishop told reporters.

About 2,500 new convicted paedophiles would be added to Australia’s sex offender register each year and would lose their passports under the new laws.

The register contains 3,200 serious offenders who will be banned from travel for life. Less serious offenders drop off the register after several years of complying with reporting conditions and would become eligible to have their passports renewed.

The justice minister, Michael Keenan, said the laws were the most comprehensive of their kind in the world.

Child welfare advocates had lobbied for the law change. They complained that, under Australian law, a bankrupt person cannot travel overseas without a trustee’s permission. But convicted paedophiles had been free to continue offending beyond the reach of Australian law enforcement.

In announcing the reform on May, Bishop said governments in the Asia-Pacific region wanted Australia to do more to stem child sex tourists.