Protesters have greeted Chinese president Hu Jintao and his wife as they arrived for a three-day UK visit.
Mr Hu is in Britain to discuss trade links with Tony Blair
The pair were ceremonially greeted by the Queen and the Duke of Edinburgh on Horse Guards Parade, central London.
Hundreds of human rights protesters and Chinese government supporters lined the area as they entered Buckingham Palace in the royal carriage.
The couple will stay at the palace and Mr Hu will visit 10 Downing Street for talks with Tony Blair.
As the state procession made its way up the Mall the Queen looked out on protesters against Chinese rule in Tibet who started chanting loudly and waving banners.
As the state coach passed, Mr Hu waved enthusiastically to his own supporters who were collected on the opposite side of the road to the protest.
Free Tibet campaigners shouted "shame on you, Mr Hu" while members of the Falun Gong spiritual movement, banned in China, largely stood in silence.
BBC News website reporter Dominic Casciani said that, after the procession had passed, police officers apprehended a single man, who had begun to wave a pro-China flag in the middle of the Tibet campaigners.
He was taken away to loud jeers, our correspondent said.
Earlier, the Queen, dressed in a red overcoat, greeted Mr Hu and his wife with lengthy handshakes on Horse Guards Parade.
Prince Philip and Mr Hu inspected the 1st Battalion Irish Guards while the Queen chatted to his wife Liu Yongqing through an interpreter.
The prime minister, Home Secretary Charles Clarke and Foreign Secretary Jack Straw joined the dignitaries on the parade ground.
Director of the Free Tibet Campaign Alison Reynolds said she hoped the demonstration would send a strong message to the visiting president.
"The point is, he gets to see the Tibetan flag, which is banned in China and Tibet.
"The message we want Tony Blair to deliver tomorrow is that Hu Jintao should meet the Dalai Lama.
"Tony Blair certainly has the influence, but whether he chooses to exercise it ... we sincerely hope our presence in the next couple of days will send a strong message."
The president was formerly party chief in Tibet where he declared martial law over protests by separatists.
Last week he urged the Dalai Lama to "renounce his Tibetan independence proposition".
The prime minister earlier said protests over China's human rights records would be free to go ahead.
Mr Blair told journalists discussions with Mr Hu would focus on the growing economic links between the two countries as well as international security issues and climate change.
During their stay, the presidential couple will attend a banquet in the presence of the Queen at Buckingham Palace and visit an exhibition of Chinese art at the Royal Academy of Arts in London.
The president and his wife are also due to fly to Germany and Spain for state visits there.
US President George Bush is due to visit Beijing later in the year.