New Zealand's Prime Minister has called the world's richest footballer David Beckham thick.

Beckham came to New Zealand in December 2008 for an Oceania All Stars exhibition match which cost the Auckland region $1.8 million, just a month after John Key was first elected prime minister.

Only 16,000 fans attended the match.

The British footballer, who now plays for the Los Angeles Galaxy team, is estimated to have earned more than $300 million from football and endorsements.

During a visit to a high school in Dunedin on Friday Mr Key joked with a group of pupils, saying his son spent 45 minutes with Beckham during the star's visit.

Mr Key said Beckham was handsome and a really nice guy to spend that long with his son, but was also "thick as batshit".

The Prime Minister's office said on Friday it had no comment to make on the matter.