THE HAGUE (AFP) - The Dutch royal family expressed regret on Wednesday (Dec 15) after it last week invited 21 people to celebrate the 18th birthday of the future queen contrary to coronavirus health guidance.

The Netherlands said on Tuesday it will close primary schools early for Christmas holidays and extend a night-time lockdown as fears grow over the Omicron coronavirus variant.

"The family strived to treat the coronavirus rules responsibly with this outdoor gathering and by taking precautions" including tests and social distancing, Dutch Prime Minister Mark Rutte wrote in a letter to parliament.

"The king informed me that on reflection it was not a good idea to organise (the gathering)."

People in the Netherlands can currently receive a maximum of just four guests over the age of 13 in their homes.

The royal gathering was held last Saturday in a park adjoining a royal palace and guests were required to be vaccinated, to test for coronavirus and follow social distancing.

Mr Rutte's letter did not specify how many people had attended but local media quoted the government as saying 21 invites were sent.

Princess Amalia celebrated her 18th on Dec 7 and was elevated to the Dutch Council of State, the government's highest advisory body, by virtue of reaching the age of majority.

The party is the latest in a string of faux pas committed by the Dutch royal household during the pandemic that have dented its popularity.

In October 2020 the royals were forced to cut short a holiday in Greece following an outcry when details were published and the Netherlands had just gone into a partial lockdown.

Amalia, the heir to the throne, made headlines in June when she gave up her right to a €1.6 million (S$2.5 million) annual income.