Around the world, there are legendary, dynastic rivalries in football.
Think Turkey versus Greece, England versus Germany and Brazil versus Argentina.
And now, as the two sides face each other in a crucial World Cup qualifier, Hong Kong and China look set to join the list of lasting football rivalries.
The two sides have been playing against each other since the 1970s, without either side much troubling the giants of the game, or each other.
But in recent months, tension between the two sides has been building.
For Tuesday's match at Hong Kong's Mongkok Stadium, local media reports that more than 1,000 police officers will be deployed.
If true, it would be an unprecedented number for a sports match in the territory.
And for the first time, Hong Kong and mainland fans will have to use separate entrances, foreign media reports.
They will also be segregated - standard practice for football matches in most parts of the world, but a novelty in Hong Kong.
Mongkok Stadium can hold around 6,000 spectators but mainland Chinese fans have been allocated only 500 tickets.
Tickets reserved for local fans sold out quickly, with the website of an online ticket seller reportedly crashing under the weight of high demand.
But fans are not the only ones making sure to book themselves a seat in the stadium.
Local and international media, and a team from Fifa, will be out in force too: watching both sides - and their fans.
Last month, football's governing body fined the Hong Kong Football Association 40,000 Hong Kong dollars ($5,160; £3,400), after local fans booed the national anthem "March of the Volunteers" during a qualifier against Qatar in September. (Foreign)
Hong Kong, as a semi-autonomous Chinese city, shares the national anthem with mainland China - but increasingly little else.
Political tension between Hong Kong and China has surged in the past five years, culminating in last year's pro-democracy "Umbrella Movement".
But the booing began only during the current World Cup campaign.