Trump welcomed to Buckingham Palace by Queen Elizabeth

US President Donald Trump and First Lady Melania Trump are meeting the Queen on the first day of their state visit to the UK.

Trump and his wife, Melania, were greeted by the 93-year-old monarch at Buckingham Palace at the start of a three-day state visit which sees him feted with the full force of royal ceremony: a formal dinner with the queen, tea with heir Prince Charles, and a tour of Westminster Abbey, coronation church of English monarchs for 1,000 years.

“I look forward to being a great friend to the United Kingdom, and am looking very much forward to my visit,” Trump wrote on Twitter as he landed at London’s Stansted Airport.

Trump arrived on Air Force One earlier on Monday and were taken to the US ambassador's home in central London, where they are staying.

Minutes before touching down, Trump criticised Mayor of London Sadiq Khan, with whom he has clashed in the past.

He tweeted that Khan - who had earlier said the UK should "not roll out the red carpet" for Trump - was a "stone cold loser", but the president added he was looking forward to his visit.

Protests are planned in several UK cities during the three-day visit, including London, Manchester, Belfast, and Birmingham.

Talks between Trump and outgoing Prime Minister Theresa May will begin on Tuesday, with the pair expected to discuss climate change and Chinese technology firm Huawei.

Crowds were gathered outside Buckingham Palace as the president and first lady landed by helicopter shortly after midday.

As he stepped onto UK soil, Trump was greeted by US Ambassador to the UK Woody Johnson and Foreign Secretary Jeremy Hunt.

Tory leadership candidate Hunt, who has spoken about the importance of the UK's relationship with the US, said Trump mentioned to him "some of his very strong views about the Mayor of London" which he had also tweeted.