Norwegian Prime Minister Jonas Gahr Støre has said he agrees with Crown Princess Mette-Marit's admission of "poor judgement" after it emerged she had extensive contacts with late sex offender Jeffrey Epstein.

The princess features hundreds of times between 2011-14, in the latest files released by the US Department of Justice relating to Epstein.

This latest embarrassment for the royal family comes on the eve of her son's seven-week trial in Oslo on 38 charges including rape and assault.

Princess Mette-Marit married Norway's Crown Prince Haakon as a commoner when her son Marius Borg Høiby was four, and is in line to become queen when her husband accedes to the throne.

As the content of her email exchanges began to emerge, the princess released a statement on Saturday saying: "I showed poor judgement and regret having any contact with Epstein at all. It is simply embarrassing."