The Queen has formally welcomed Chinese president Xi Jinping to the UK for a state visit expected to herald closer ties between Britain and China.
The pomp and pageantry of the Armed Forces' prestigious ceremonial units were on display to greet the Chinese leader whose visit has been hailed by David Cameron as an "important moment'' in the relations between the two nations.
Mr Xi's four-day trip is expected to set the seal on more than £30 billion of trade and investment deals.
But the Prime Minister is facing pressure to raise with the president concerns about China's human rights record, and the "dumping" of cheap steel - which is blamed for the loss of thousand of British steel jobs in the last few days.
Critics have warned that Britain will "rue the day'' it forged deeper ties with China and accused the Government of acting like a "panting puppy'' in its relations with the country.
But Foreign Secretary Philip Hammond insisted the move was in the national interest.
Commons Speaker John Bercow appeared to obliquely criticise China on the day its president addressed both Houses of Parliament.
Intervening during a question in the Commons comparing the UK's relationships with China and India, ahead of Indian prime minister Narendra Modi's visit to the UK next month, Mr Bercow said: "And of course the Indian prime minister is the representative of a great democracy."
The Speaker is the highest authority in the Commons and represents the chamber to the Queen, and after his comment there were audible intakes of breath.
At London's Horse Guards Parade - Henry VIII's former jousting yard - the Queen and the president shook hands.
Mr Xi had arrived with the Prince of Wales in a chauffeur-driven limousine and behind them in another car was the Duchess of Cornwall and the president's wife Peng Liyuan.
The muffled sound of a 41-gun royal salute rang out as the King's Troop Royal Horse Artillery in nearby Green Park, fired the welcoming volleys.
The Queen introduced the president to leading figures from her Government and national life including Mr Cameron, Home Secretary Theresa May, Alan Yarrow, the Lord Mayor of the City of London and Metropolitan Police Commissioner Sir Bernard Hogan-Howe.
On the parade ground before them was a guard of honour comprising 96 rank and file men and three officers from 1st Battalion Grenadier Guards.
Major Benjamin Jesty, captain of the guard of honour, marched forward and presented his men giving the order in Mandarin.
Speaking the language he has been practising for a number of weeks he said: "The Guard of Honour of 1st Battalion Grenadier Guards is present, formed up and ready for your inspection, sir."
The Duke of Edinburgh joined the Chinese leader as he walked past the two rows of guardsmen wearing their scarlet tunics and bearskins.
After the welcoming ceremony the two heads of state, senior members of the Royal Family and leading figures from China's government left Horse Guards Parade in a glittering carriage procession for Buckingham Palace.
As they travelled along The Mall protesters from the Free Tibet campaign group booed as the carriages passed, while rival pro-China supporters played the Chinese national anthem through their mobile phone via a megaphone.