Chinese dissident Liu Xiaobo was awarded the Nobel Peace Prize in an Oslo ceremony derided by Beijing as a political farce, and dedicated it from his prison cell to the "lost souls" of the 1989 Tiananmen Square crackdown.
US President Barack Obama, a Peace Prize laureate last year, called on Beijing for the prompt release of 54-year-old Liu, who was jailed last year for 11 years for subversion.
In Beijing, police stepped up patrols at key points on Friday, including Tiananmen Square, where witnesses say hundreds or thousands were killed when troops crushed reform protests, and Liu's apartment where his wife is believed to be under house arrest. Authorities tightened a clampdown on dissidents.
Western news websites, including the BBC and CNN, appeared to have been blocked. But there were no signs of trouble in the Chinese capital where memories of Tiananmen have faded for many as China has risen as a global economic and political power while guarding the Communist Party's tight hold on society.
"We can to a certain degree say that China with its 1.3 billion people is carrying mankind's fate on its shoulders," Norwegian Nobel committee chairman Thorbjoern Jagland said at the ceremony in Oslo's grey-walled City Hall.
The thousand guests rose to a standing ovation when he called for Liu's release.
"If the country proves capable of developing a social market economy with full civil rights, this will have a huge favourable impact on the world. If not, there is a danger of social and economic crises arising in the country, with negative consequences for us all."
The absence of the laureate was symbolised at the ceremony by an empty chair and a large portrait of Liu, bespectacled and smiling. After his speech, Jagland placed the Nobel award on the chair, amid applause.
It was the first time that a laureate under detention had not been formally represented since Nazi Germany barred pacifist Carl von Ossietzky from attending in 1935.
Norwegian actress Liv Ullmann read out an address made by Liu, who was closely involved in Tiananmen and more recently helped found the reform group Charter 08, to a court during his trial for subversion in December 2009.
"Hatred can rot away at a person's intelligence and conscience. (The) enemy mentality will poison the spirit of a nation, incite cruel mortal struggles, destroy a society's tolerance and humanity, and hinder a nation's progress toward freedom and democracy," the address said.
But the former literature professor saw cause for hope.
"I, filled with optimism, look forward to the advent of a future, free China. For there is no force that can put an end to the human quest for freedom, and China will in the end become a nation ruled by law, where human rights reign supreme."
Jagland said Chinese attempts to control the internet showed its weakness. "Information technology cannot be abolished. It will continue to open societies."
"Liu has told his wife that he would like this year's Peace Prize to be dedicated to 'the lost souls from the 4th of June.' It is a pleasure for us to fulfil his wish."
The Peace award, as often in the past, has stirred international diplomatic conflict, with China accusing the Committee of representing the interests of arrogant Western nations who seek to impose their ideas on an unreceptive world.
"The facts fully show that the Nobel Prize Committee's decision does not represent the majority of the world's people, especially the will of most developing countries. Prejudice and lies will not stand," the Chinese Foreign Ministry said.
China, drawing on its growing economic clout in the world, has mounted what the Committee calls an unprecedented campaign to encourage countries to boycott the ceremony.
China declared that the "vast majority" of nations would boycott but the Norwegian award committee said two-thirds of those invited would attend. [ID:nTOE6B6062]
Among the countries not attending were Russia, Kazakhstan, Saudi Arabia, Argentina, Tunisia, Pakistan, Serbia, Iraq, Vietnam, Iran, Afghanistan, Egypt, Sudan, Cuba, Morocco and Algeria.
Both the speaker of the U.S. House of Representatives, Nancy Pelosi, and House foreign affairs committee member Chris Smith said they would attend the ceremony after the House's 402-1 passage of a bill calling on China to release Liu.
"Sadly, the Chinese government shares with the governments of Nazi Germany and the Soviet Union the terrible distinction of being the only governments of major nations to block a Nobel Peace Prize recipient from accepting the prize," Smith said in a statement. He said he was "outraged that nearly 20 nations have been strong-armed by China to boycott the ceremony."
Liu's fame overseas was lost on most residents in Beijing, where memories of the 1989 crackdown on pro-democracy protesters have faded.
"Everything is different now since the revolt of 1989. People's ideas have changed. China has changed," said businesswoman Ma Junpeng. "People like Liu are irrelevant."