A former electrician has left his old life behind to go undercover as a fake paedophile to save children from sex slavery.

Tony Kirwan, from Queensland, has rescued almost 2000 children while working for the charity he founded 17 years ago, Destiny Rescue, in Southeast Asia.

Mr Kirwan now trawls the brothels and karaoke bars of a Manila red light district, looking for underage girls to rescue.

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Mr Kirwan now trawls the brothels and karaoke bars of a Manila red light district, looking for underage girls to rescue

Queenslander Tony Kirwan (pictured) has rescued almost 2000 children while working for the charity he founded 17 years ago, Destiny Rescue, in Southeast Asia

'We're looking for girls a bit younger than this. Getting fussy in me old age,' Mr Kirwan tells a Swiss tourist while accompanied by SBS's Dateline.

Mr Kirwan and his team wear hidden cameras to free children who have been coerced into working in the sex trade.

At one bar Tony tells the mamasan the young girls, and is given a phone number to call.

The Destiny Rescue team then pass on that information to the local police, whose anti-trafficking unit relies on help from NGOs to put a dent in the sex trade.

After rescue comes rehabilitation, while the Christian charity working to stop sex trafficking victims from returning to prostitution.

The key to the rescues is trust, Mr Kirwan said, convincing the girls they are good people while the pimps still think they are paedophiles.

Mr Kirwan and his team wear hidden cameras to free children who have been coerced into working in the sex trade

'You're definitely role playing. To the bouncers or the mamasan, you want to look like a normal customer,' Mr Kirwan told Dateline journalist Amos Roberts.

'To the child you want to look totally different to every other customer that she's ever sat with. So it's this balancing act of, of just acting all the time.'

Mr Kirwan said he had to overcome his own innocence to be able to do the work, saying it was hard for him to even walk into a brothel.

Almost two decades later his work is paying off, and Destiny Rescue is active in the Philippines, Cambodia, India and Thailand.

The charity aims to rescue 100,000 children from sex trafficking by 2020 with the help of hundreds of volunteers and employees worldwide.