Opening ceremonies at the Beijing Olympics are exactly one year away, but Chinese officials are still battling polluted air and fears over unsafe food.

A two-hour celebration was held in Tiananmen Square, the sprawling plaza in the heart of the capital on Wednesday as the countdown to the Beijing Games reached the one-year mark.

More than a million Chinese gathered in parks throughout Beijing for dawn exercises as they launched the countdown to the 2008 Games.

Test events, for sports such as hockey and rowing, also got underway at the venues that will hold those competitions

The celebration's centrepiece came as 10,000 invited guests, including national leaders, celebrities and Olympic chiefs, gathered on Tiananmen Square to celebrate the countdown.

Dancers cavorted in glamorous garb, pop singers belted out the theme song "We're Ready" and fireworks coloured the sky as revellers counted down to 8:08 pm, which is exactly one year away from the 2008 Olympics.

Eight is a lucky number for the Chinese and so the Games will begin at 8:08 p.m. on August 8, 2008.

International Olympic Committee president Jacques Rogge told the crowd that Beijing organizers had worked "extremely hard to give Beijing an Olympic shape.''

"The world is watching China and Beijing with great expectations. The athletes also have great expectations and they are all looking forward to competing in the state-of-the-art Beijing venues,'' Rogge said.

"Beijing and China will not only host a successful Games for the world's premier athletes, but will also provide an excellent opportunity to discover China, its history, its culture and its people, with China opening itself to the world in new ways,'' he said.

"From what we have seen so far, the preparations for Beijing 2008 are truly impressive in every regard. I don't think we have ever seen preparations on this scale.''

Australian IOC member John Coates has advised his country's athletes to minimize their time in China, by arriving as close to the Aug. 8, 2008 start as possible.

"We will be not recommending a long period in China before the games," Coates told The Associated Press.

"That only is going to increase the possibility of respiratory or gastric illness -- particularly if you are not living in the village."

But Coates added he was less concerned about unsafe meals. Chinese officials have said they would spare no expense to protect athletes against tainted food.

"The IOC pays very special attention to the quality of food in the Olympic Villages," said Coates. "We don't expect that to be a problem, but we will still be advising our athletes to eat in the village, not in local food stores. Be careful with bottled water and take every precaution."

According to Chinese news agency Xinhua, vice commerce minister Gao Hucheng has blamed food concerns on the media.

"We are completely opposed to this type of hearsay, generalised, made-up, malicious reports," he said.

Problems with air quality could prove harder to counter, although organizers have taken decisive action. For the first half of this month, one million cars will be pulled from Beijing's streets.

China also faces renewed pressure over its human rights record, and activists are using the Olympics to draw attention to various causes.

Three Canadians have been detained after apparently helping to unfurl a banner over the Great Wall that read: "One World, One Dream, Free Tibet 2008."

The Canadians, who were detained on Tuesday, were identified as Melanie Raoul and Sam Price, both of Vancouver. A third Canadian activist, Lhadon Tethong, was picked up on Wednesday.

Despite the criticism, howver, there is excitement in Beijing over the upcoming Olympics, and early achievements are already gaining praise.

The National Stadium, nearing completion, has been hailed as an architectural triumph. Massive metal bars wrap around the structure, earning it comparisons to a bird's nest.

But it would be home to a very large bird. Officials say it will be the biggest enclosed space in the world.

Training facilities for athletes also look to be a success. Unlike previous Olympics in recent memory, for example, gymnasts will be able to practice in the exact same conditions they'll face in actual competition.