China mixed politics and sport with a boldness unseen since the Cold War on Friday, with President Xi Jinping announcing a new alliance with Russia's Vladimir Putin just hours before presiding over a spectacular Olympics opening ceremony.

Held in the famed Bird's Nest stadium before a crowd thinned out because of COVID-19, the opening ceremony easily cleared the high hurdle of spectacle expected of China. Three thousand performers took to a stage comprised of 11,600 square metres of high-definition LED screens.

Dancers poured into the stadium waving glowing green stalks to mark the first day of spring on the Chinese calendar, followed by an explosion of white and green fireworks that spelled the word "Spring".

Lasers carved imagery from each of the previous 23 Winter Games. The block was then "broken" by ice hockey players, enabling the Olympic rings to emerge, all in white.

During the traditional "parade of nations", competitors from "Hong Kong, China" were met with cheers - as were those from the "Russian Olympic Committee" - the name used by the Russian delegation while the country is officially banned for doping.

Triumphant fireworks were launched into the night sky after Xi declared the games open. But the most consequential pyrotechnics may have come hours before the ceremony, when Xi and Putin unveiled their alliance, proclaiming friendship between their countries with "no limits".

It was a stark reminder that the games were being held on a backdrop of geopolitical rivalry unseen since the tit-for-tat Cold War boycotts of the 1980s, when the United States refused to attend the Olympics in Moscow and the Soviet Union stayed away from Los Angeles.

With tensions on both sides of the Eurasian land mass at their most taut for decades, Putin and Xi publicly took each other's sides over a range of grievances, most notably Ukraine, where the West accuses Putin of preparing for war.

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As in Japan just half a year ago, the COVID-19 pandemic imposed severe constraints. With China still sticking to a "zero Covid" policy despite the Omicron variant spreading fast across the globe, organisers decided last month not to sell tickets to Olympic events. A "closed loop" separates competitors and other personnel from the Chinese public.

But talk of war in Europe and escalating rivalry in Asia meant that COVID was hardly the biggest distraction from sport. The United States and other countries have declined to send dignitaries to Beijing, citing alleged human rights abuses, which Beijing denies.

China's role in global sport has also been under a harsh glare in recent months over the case of tennis player Peng Shuai. The women's tennis tour cancelled events in China saying it feared for her safety after she appeared to accuse a senior official of sexual assault. Chinese media have shown Peng making public appearances, including a video phone call last year with International Olympic Committee boss Thomas Bach.

Because of the pandemic, the dignitaries visiting for the Olympics were the first to make official trips to Beijing in more than two years. The guest of honour was clearly Putin.

The Russian leader - who hosted his own winter Olympics in 2014 just days before sending troops to seize Ukraine's Crimean peninsula - thanked Xi for inviting him, adding: "We know firsthand that this is a huge job."

In a joint Russian-Chinese statement, Beijing backed Russia's longstanding call for NATO to halt its expansion - Moscow's central demand in a dispute with Western countries that say they believe Putin is preparing for war in Ukraine.

Russia, which has deployed more than 100,000 troops to the Ukrainian frontier, denies planning to invade but says it could take unspecified military action unless demands are met, including barring Ukraine from ever joining NATO.

Moscow, for its part, said it fully supported Beijing's stance on Taiwan and opposed Taiwanese independence in any form.