China celebrated the Olympic flame's arrival on Monday but a thick blanket of security highlighted concerns that protests over Tibet, human rights and other issues may tarnish the historic torch relay.
The flame arrived from Greece on Monday morning ahead of what will be an epic journey through 19 countries, before it returns to China for a three-month tour.
The relay is being billed as the most ambitious of all time with the "high point" being an ascent of Mount Everest in May. It will be the longest ever, lasting 130 days and covering 137,000 kilometres (85,000 miles).
China was due to stage a nationally broadcast welcoming ceremony from Tiananmen Square, the political heart of Beijing, late on Monday morning, with 5,000 specially selected people brought in for the celebrations.
President Hu Jintao was expected to attend the ceremony, the Beijing Olympic organising committee said.
However tight security at the Beijing airport for the flame's arrival and at Tiananmen Square showed that China's communist rulers were working overtime to ensure that the torch relay would not be marred by protests.
Activist groups have warned they intend to use the torch relay to highlight their many concerns over China, including the crisis in Tibet, Beijing's close ties with the government in Sudan, and domestic human rights issues.
Of these, the highest profile issue on the global agenda is Tibet, where a crackdown on three-weeks of protests against Chinese rule of the Himalayan region has raised concerns among world leaders.
Protests in the Tibetan capital, Lhasa, on March 10 to mark a failed 1959 uprising against Chinese rule escalated into widespread rioting in the city, which then spread to neighbouring Chinese provinces populated by Tibetans.
Beijing says rioters killed 18 civilians and two police officers. Exiled Tibetan leaders have put the death toll from the Chinese crackdown at 135-140 Tibetans, with another 1,000 injured and many detained.
Despite the massive security presence in Lhasa, there was a fresh protest there on Saturday, according to the International Campaign for Tibet and the Free Tibet Campaign.
In Beijing, authorities closed off Tiananmen Square -- the scene of democracy protests in 1989 that the military infamously crushed -- on Sunday night ahead of the torch ceremony.
Security personnel could be seen on the surrounding buildings on Monday, and the nearby subway stations had been closed off to prevent any unauthorised people intruding on the ceremony.
And while Chinese state-run television said its broadcast of the Olympic flame's arrival at Beijing airport was "live", the footage appeared to be shown with a delay of about one minute.
Last Monday, CCTV also cut away from the Olympic flame lighting ceremony in Greece as protesters tried to disrupt a speech given by China's Olympic organising committee chief, Liu Qi.
Olympic officials said students, workers, performers and VIPs were among the 5,000 people invited for the ceremony.
Among those were groups of cheer squads who were seen on television ahead of the ceremony waving the Chinese and Olympic flags.
Although the flame welcoming ceremony was to be held on Monday, the relay officially starts on Tuesday when the sacred flame is scheduled to depart for Almaty, the capital of Kazakhstan.
Pro-Tibet activists and other groups are planning demonstrations at key locations along the way, including London on April 6, Paris on April 7 and San Francisco on April 9, the only stop in the United States.
Other potential trouble spots include New Delhi on April 17. The Chinese government has already approached India about security arrangements.