Hong Kong - Hong Kong fans booed the anthem they share with China on Tuesday while some turned their backs and held up "boo" signs in a show of defiance before a crunch World Cup football qualifier with their mainland rivals.
Home supporters also swore at the visiting Chinese supporters and showed them their middle fingers in a rowdy start to proceedings at the sold-out, 6,000-seat Mong Kok Stadium.
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Loud jeers rang out during the "March of the Volunteers" anthem, which the semi-autonomous territory shares with China, and held up white signs saying "boo" in English, following warnings against audible jeering.
The joint 2018 World Cup and 2019 Asian Cup qualifier follows last year's "Umbrella movement" pro-democracy protests which gripped the city and underlined discontent over Beijing's rule.
The fans have been strictly segregated, using separate entrances and even different toilets, in a bid to head off any potential trouble in a district which was one of the centres of the pro-democracy protests.
"Because we don't like the Chinese national anthem, we have to go against it," Hong Kong student Jerry Wong, 20, told AFP. "Because Hong Kong is not part of China, I don't feel like I am Chinese."
The booing was also in defiance of orders from world body FIFA, which fined the Hong Kong Football Association after fans jeered their own anthem at previous qualifiers.
Chinese supporter and government worker Fan Yufeng, 33, who crossed the border to watch the game, said the spectators who showed anti-China feelings did not speak for all of Hong Kong.
"They only represent a small portion of Hong Kong," he told AFP.
Local media reported that 1,200 police officers would be on standby for the match, or about one for every five fans at the stadium.
But despite tensions between the fans, after the anthem both sides held a moment's silence to commemorate the victims of the weekend attacks in Paris.
The match is critical to both Hong Kong and China's chances of reaching the 2018 World Cup in Russia as they lie second and third respectively in Group C, after drawing 0-0 under heavy security in Shenzhen in September.