SHANGHAI (AFP) - It was 50 years ago, but Mr Zhang Xielin still remembers vividly how a shaggy-haired American table tennis player stepped onto the Chinese team's bus, a chance encounter which would shape history.

It was the world championships in Nagoya, Japan, and Mr Glenn Cowan had mistakenly hopped in with Mr Zhang and his teammates - an awkward moment because the United States and China were then deeply at odds.

"We were on the bus and were talking and laughing," Mr Zhang, now 80, told AFP.

"But when we realised that an American had come onto the bus, we fell silent."

The Chinese triple world champion Zhuang Zedong eventually came forward and famously broke the ice, giving Mr Cowan a silk embroidery as a souvenir from China.

They did not know it at the time, but it was the spark for China and the US to begin normalising relations, in what became known as "ping-pong diplomacy".

Mr Zhang, a doubles world champion and later China's coach, recalled: "Mr Zhuang understood that there was a difference between the American people and the American government, and that we should be nice to American people, so he took the initiative to chat with Glenn."

Photographers captured Mr Zhuang and a 19-year-old Cowan shaking hands and smiling.

"The newspaper came out the next day and it seemed that China and the United States were about to have a relationship," said Mr Zhang.

Days later, on April 10, 1971, the US team became the first Americans to step foot in China for nearly a quarter of a century when they were invited to play friendly matches in the country.

The thaw saw President Richard Nixon visit China in February 1972, and a Chinese table tennis squad visit the US.

In 1979, formal relations were established between the two countries.

'Compete peacefully'

Mr Yao Zhenxu played against Mr Cowan, who died in 2004, during the Americans' ground-breaking trip.

Mr Yao still remembers the score, he won 21-12, 21-14, and says that Mr Cowan thanked him afterwards for "a serious game".

The American team were vastly inferior to the Chinese, so the hosts sometimes let their visitors win points in the spirit of sportsmanship and goodwill.

Now 74, Mr Yao says that it was only afterwards that he realised that he had played a part in something historic.

"Because of ping-pong diplomacy, we changed the world order, and the people of China and the United States started friendly exchanges," he said.

Mr Yao appeared alongside Mr Zhang in Shanghai on Saturday to mark 50 years of ping-pong diplomacy, with the city authorities hosting an event with speeches and friendly amateur matches.

But the anniversary comes at a time when relations between Washington and Beijing have deteriorated markedly over a number of issues, notably trade, the fate of China's Uighur minority and a clampdown in Hong Kong.

In a recorded speech to mark the 50th anniversary, China's ambassador in Washington, Mr Cui Tiankai, accused some in the US of "ideological bias and zero-sum thinking".

But he and Chinese state media took a largely positive tone, with Xinhua news agency hailing ping-pong diplomacy's "wonderful legacy".

Mr Yao and Mr Zhang hope that the spirit of 1971 can help shape future relations between the world's top two economies for the better.

"Everyone knows that the relationship between China and the United States is a bit tense nowadays," said Mr Yao.

"We hope that we can agree to disagree and keep friendly relations.

"Don't be afraid of competition, we can compete peacefully."