Hong Kong soccer fans told not to turn crucial World Cup game against China into a political football

Hong Kong soccer fans have been warned they risk scoring an own goal if they turn tonight's crunch World Cup qualifier against China into a political football - with those who do anything deemed to "endanger national security" facing being locked up for nine days.

The warning came from Shenzhen authorities ahead of tonight's big game at the city's Baoan Stadium, which 2,200 Hong Kong fans are set to attend.

The timing is sensitive, as it falls on the day the nation marks the 70th anniversary of Japan's surrender in the second world war with a military parade in Beijing.

It also comes after Hong Kong supporters jeered the national anthem during the first two qualifiers at Mong Kok Stadium, as soccer became the latest point of discord between city and nation and an outlet for Honkongers to vent their grievances against mainlanders and Beijing.

At least 1,000 police officers will be on duty tonight, and the Shenzhen Public Security Bureau yesterday issued a "gentle reminder" that fans who failed to behave could be warned, punished with a fine of up 200 yuan (HK$240) or detained. They could be held for a period "longer than five days but shorter than 10 days" and fined up to 500 yuan.

Fans could get into trouble, the bureau said, if they showed disrespect to the national anthem or flag, or if they wore clothes or displayed banners or flags deemed to "endanger national security". All fans will have to present their identity documents to get into the stadium.