Prime Minister Jacinda Ardern will have her audience with the Queen in London tonight as the Commonwealth Heads of Government meeting kicks off at Buckingham Palace.

Ardern will spend most of today at Buckingham Palace, with the "family photo" in the ballroom, the official opening of CHOGM and a reception tonight for the new leaders in the Commonwealth, and a private audience with the Queen, which will be their first meeting.

Ardern, who lost her cat Paddles last year, may be able to offer a sympathetic ear to the Queen whose last corgi - Willow - died on Sunday.

It follows a hectic day in London overnight in which Ardern was to meet with four of the Five Eyes leaders - British PM Theresa May, Canada's Justin Trudeau and Australia's Malcolm Turnbull. The meeting was convened by May to discuss an alleged cyber-espionage attack on governments, infrastructure providers and businesses, which Russia has been blamed for.

Ardern also spoke to youth at City Hall with Trudeau and London Mayor Sadiq Khan, had an audience with Prince Charles and Camilla at Clarence House, and met Fiji's Prime Minister Frank Bainimarama for the first time before heading to Downing St to meet May.

The day ended with a welcome reception hosted by May for more than 50 leaders in London for the CHOGM summit.

There is a poignant symbolism about it being in London this year - it is expected to be the Queen's last CHOGM, an event she had always attended apart from in 2013 when she instead sent Prince Charles to Sri Lanka.

It is also perfect timing for May who is set to seek support in the case against Russia over the use of a nerve agent against former Russian spy Sergei Skripal and his daughter Yulia. While some have already expressed support, including New Zealand, others are more reluctant, such as India.

May will also be looking for close friends as Britain prepares to leave the EU - while New Zealand is already in the line, other countries are likely to want to join the queue for free trade agreements.

London was dressed to impress - the Mall and Buckingham Palace were bedecked with the flags of the Commonwealth and even the weather was working to Her Majesty's orders - sun was expected all week after a long winter.

Between the pomp, the feasts and the royals the leaders will grapple with the issues that beset the group.

There will be a big turnout - all but two of the 53 countries in the Commonwealth are represented by their leaders - including India's Narendra Modi, who has skipped the last few CHOGMs.

Tomorrow the leaders will go into a retreat at Windsor Castle but on the sidelines until then major international issues will also be playing out - most of which do not involved a Commonwealth nation but rather the United States and Russia.

The hot topics in leaders' conversations are expected to address attempts to get UN action on the use of chemical weapons in Syria, and May's call for Russia to be condemned over the nerve agent case.

The "trade wars" threatened by US President Donald Trump's new tariffs could also re-ignite debate about a "Commonwealth Trade Area", something NZ First leader Winston Peters supports but which would be complicated and tricky given the diversity of the countries involved.