Jill Biden joins Rishi Sunak's Downing St Coronation Big Lunch

William and Kate visit crowds in Windsor gathering after King Charles III's crowning

Follow the latest news from the coronation of King Charles here

US first lady Jill Biden was a surprise guest at Downing Street for the Big Lunch on Sunday, as thousands of coronation street parties for members of the public took place across Britain.

Prime Minister Rishi Sunak and his wife opened the door to volunteers, Ukrainian refugees and youth groups in Downing Street for a lunch to mark the coronation.

Mr Sunak and his wife Akshata Murty hosted the event on Sunday.

Mr Sunak and Mrs Biden greeted each other with a kiss on both cheeks.

They stood chatting as many invited guests took photos before taking seats right in front of the No 10 door.

“Come rain or shine, thousands of friends and neighbours are coming together this weekend to put up the bunting, pour the tea and cut the cake at street parties and community events across the UK,” Mr Sunak said.

More than a million people signed up after being urged to get involved in the community gathering, which is one of the centrepieces of the coronation bank holiday weekend.

Those looking to take part can use an interactive tool to find the nearest Big Lunch location available in their area. Bakers and baking business owners across the country put their skills to the test creating cakes to celebrate the coronation.

Organisers have also created an information pack for guests which outlines conversation pointers for those who may be affected by social nerves.

The Coronation Big Lunch - in pictures

Britain's Prime Minister Rishi Sunak offers a plate of sandwiches to US first lady Jill Biden during a coronation Big Lunch in Downing Street. PA

Musicians play during a Big Lunch celebration in London. AP

Members of the public enjoy the coronation weekend next to Battersea Power Station in London. Getty Images

The Coronation Carnival Parade makes its way along the promenade during celebrations in Morecambe. Reuters

Residents attend a street party in Chiswick, West London. AFP

Prince Edward, the Duke of Edinburgh, arrives for the Big Lunch in Cranleigh, Surrey. PA

People celebrate Britain's King Charles' coronation with a Big Lunch at Regent's Park in London. Reuters

Sophia, three, laughs as she is thrown up in the air during The Big Lunch at The Long Walk in Windsor. Getty Images

A member of the public wears a crown at the Coronation fete in Redruth, Cornwall. Getty Images

Women take selfies at The Big Lunch in Windsor. Getty Images

A cypher for King Charles is seen on the grass next to people celebrating the Big Lunch on the prom, in Morecambe. Reuters

People get ready for the Big Lunch in Windsor. Getty Images

A child has a Union Jack flag painted on his face for a party in St James' Church in London. Reuters

People dressed as kings make their way to The Big Lunch in Windsor. Getty Images

A volunteer sets up tables and chairs for the Big Lunch in Regent’s Park. Getty Images

The “conversation menu” suggests asking fellow residents whether they have met a member of the British royal family, or what their favourite way is to spend a bank holiday.

The “menu” also includes jokes to break the ice.

So far about 7,000 street parties and other events have been registered, and organisers are hoping that more will be added.

More than 17.2 million people took part in Big Lunch events last June as they celebrated Queen Elizabeth II’s platinum jubilee.

A Buckingham Palace spokeswoman said big lunches will take place from Saturday to Monday “in a nationwide act of celebration and friendship”.

UK's Prime Minister hosts coronation Big Lunch - video

On Sunday, Prince Edward and his wife Sophie attended a big lunch in Cranleigh, Surrey, while Princess Anne, the Princess Royal, and Vice Admiral Sir Tim Laurence visited a community street party in Swindon, Wiltshire.

Sunday is forecast to be the hottest day of the year so far for some parts of the UK, a change after the heavy downpours that threatened to dampen celebrations on Saturday.

A highs of 23°C is forecast for the East Midlands and down to London, beating the high of 21.2°C on April 17.

Some showers are predicted across eastern England and Scotland, but the vast majority of the country can expect sunny spells throughout the day, the UK's Met Office said.