World Athletics chief Sebastian Coe believes some cases of young athletes switching allegiance between countries before he tightened the rules last year were all but indistinguishable from human trafficking.

The new rules prevent anyone under the age of 20 from changing allegiance and demand athletes prove their ties to their new nation after a three-year waiting period.

"It's not an easy thing for me to say, but I was finding it quite hard to see a difference between what was emerging and human trafficking," Coe told Sydney's Daily Telegraph.

Something is wrong, he said, "when you have a system where two federations could effectively shake hands behind closed doors and an athlete, with very little guarantee on either side of the protocol around that transfer, could suddenly end up competing for a completely different country."

The practice of athletes from nations with an abundance of talent, such as Kenya in long-distance running or Brazil in football, switching to represent wealthier nations has become an increasing feature of sport since the start of the century.

Turkey's team at the 2016 European Athletics Championships featured seven athletes from Kenya, two from Jamaica, an Ethiopian, a Cuban, a Ukrainian, a South African and an Azerbaijani.

Without singling out any particular cases, Coe said he had become increasingly concerned about young athletes moving away from their home countries, often without parental support.

"Some of them were barely older than anything that would in any country constitute adulthood, and in some occasions barely at the age of consent," he recalled.

"And that's when I looked at this and thought we also have a responsibility here in the safeguarding space."