Warning: This article contains content that may disturb some readers.

An international think-tank has revealed an explosive new theory about what happened to missing British toddler Madeleine McCann - she was kidnapped by an international paedophile gang.

Madeleine disappeared from the holiday apartment her family was staying at in Portugal in 2007, and hasn't been seen since.

The shocking allegations were made by John Whitehead, president of conservative human rights organisation Rutherford Institute and an expert on child sex abuse.

He believes she was taken by a sex trafficking gang the same way other children are taken.

"Oh I think she was. Kids are being snatched all over the world," Whitehead told UK tabloid the Daily Star.

"When you look at migrant children coming across the border in the US, they just go missing.

"It's big business. You can get more money than from drugs and guns because you have kids doing multiple sex acts a day and they're being filmed. A child might be raped up to 6000 times in a five-year period of servitude and it's all money."

His comments come as Portuguese detectives investigate a convicted paedophile who was in the country at the time.

Officials have reportedly identified a German man who was in Portugal at the same time Madeleine disappeared.

Newshub.