BEIJING (AFP) - The Olympic torch headed for Kazakhstan on Tuesday for the first leg of an epic world tour designed to drum up enthusiasm for the Beijing Games but also certain to draw more protests.

A chartered Air China plane took off about 10:00 am (0200 GMT) to carry the torch from Beijing to Almaty in Kazakhstan, where the first leg of the relay will be run on Wednesday, a Beijing Olympic organising committee official said.

Tight security surrounding the torch highlighted concerns that protests over Tibet, human rights and other issues may tarnish its journey around the world.

President Hu Jintao officially set the flame off on its globe-trotting trip at a nationally televised ceremony from Tiananmen Square, Beijing's political heart, after it arrived from Greece earlier Monday.

The 130-day relay, hailed as the most ambitious ever, will cross 19 countries before returning to China for a three-month tour that includes an ascent of Mount Everest.

"I declare the start of the torch relay of the Beijing Olympic Games," said Hu, holding aloft the torch before passing it to Liu Xiang, a Chinese sporting icon who is the reigning 110m hurdles Olympic and world champion.

China's newly appointed Vice President Xi Jingping, widely tipped to eventually succeed Hu, used the ceremony to welcome the world to the Chinese capital for the August 8-24 Games.

"The modern Olympic Games are a great event of peace and friendship for people around the world," said Xi.

"The Chinese government and people warmly welcome athletes and friends from all countries and regions to come to Beijing for the grand Olympic event."

But thick security showed that China's communist rulers were worried about the kind of trouble that dogged the torch on its journey around Greece last week and threatens to take the shine off Beijing's Olympic showpiece.

Activist groups have warned they will use the relay to highlight concerns over China, including the crisis in Tibet, Beijing's ties with Sudan, and domestic human rights issues.

A protest by media rights group Reporters Without Borders disrupted the lighting in Greece last week in protest at China's restrictions on the press.

Tibetan and other activists tried to disrupt a ceremony in Athens on Sunday when Greece passed the torch to Beijing organisers.

Amid this backdrop, Chinese authorities sealed off Tiananmen Square -- the scene of 1989 democracy protests that were crushed by the military -- on Sunday night ahead of the torch ceremony.

Security personnel were seen on surrounding buildings and in the crowd on Monday, while nearby subway stations were closed off.

The square was open only for about 5,000 people, selected guests and performers.

In Tibet, Beijing's crackdown on three weeks of protests against Chinese rule has left 18 civilians and two police officers dead, according to China's count.

Exiled Tibetan leaders have put the death toll at 135-140 Tibetans, with another 1,000 injured and many detained, prompting international concern.

The torch will pass through Tibet for the Everest leg in May, and then again when it goes through Lhasa in June. Chinese officials have already pledged tight security for the Tibetan portions of the relay.

Pro-Tibet activists and other groups have said they are planning protests at relay locations including London on April 6, Paris on April 7 and San Francisco on April 9.

Another potential flashpoint is New Delhi on April 17. India is home to the Tibetan spiritual leader the Dalai Lama and many other exiled Tibetans.

Coinciding with the Monday's ceremony, about 150 people staged a pro-Tibet rally in Sydney while 100 Tibetan protesters were detained in Kathmandu.

After the protest at the lighting of the flame in Greece last week, Chinese state-run television broadcast Monday's ceremony -- and the flame's arrival at Beijing airport -- with a delayed telecast.

This was apparently to ensure the broadcast could be censored if there was a protest.

The torch heads to Almaty, Kazakhstan, on Tuesday, for the first relay leg on Wednesday.

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