Prime Minister Jacinda Ardern has met with Queen Elizabeth at Buckingham Palace and has been chosen to deliver the toast at a state banquet packed with royalty and other leaders in Buckingham Palace.

Ardern and partner Clarke Gayford met with the Queen in her sitting room at the Palace early this morning.

Ardern was one of only four leaders at the Commonwealth Heads of Government meeting to be granted an audience with the Queen.

Jacinda Ardern, and her partner Clarke Gayford are greeted by Britain's Queen Elizabeth II during a private audience at Buckingham Palace in London. Photo / AP

She will also attend a banquet at about 7.30am NZ Time at which Ardern will deliver a toast to the Commonwealth.

She is expected to wear a korowai [cloak] to that dinner and will end her toast with a Maori proverb: 'what is the most important thing: he tangata, he tangata, he tangata." (It is people, it is people, it is people.)

It will follow her first meeting with the Queen.

Ghana has been chosen to deliver toast to the Queen at the banquet which about 16 members of the Royal family will attend as well as more than 50 leaders and their partners.

Earlier at the formal opening of the Commonwealth Heads of Government Meeting the Queen had put in a plea for leaders to allow Prince Charles to succeed her as head of the Commonwealth when he takes over as King.

Leaders are due to decide on that role at the retreat tomorrow because there are no rules which specify who the Head of Commonwealth should be.

Prime Minister Jacinda Ardern meets British PM Theresa May at 10 Downing Street in London. (Photo / pool)

That had prompted some to suggest it should be abandoned altogether, become an elected position or rotated around the member states rather than simply pass on to the next monarch. It is a largely symbolic role but the Queen has held it since 1947 when she was 21.

Addressing the leaders, the Queen said she remembered the day she took on the role.

"It remains a great pleasure and honour to serve you as Head of the Commonwealth and to observe with pride and satisfaction that this is a flourishing network.

It is my sincere wish that the Commonwealth will continue to offer stability and continuity for future generations and will decide that one day the Prince of Wales should carry on the important work started by my father in 1949."

Ardern has said New Zealand will support it passing on to the monarchs.

It is likely to be the Queen's last attendance at a CHOGM as she hands over travel to Charles.

The Queen began by saying that after years of visiting other countries for the summit "it is a pleasure this time to welcome you to my own home."