But there is another, distinctly unofficial, national song in Singapore these days. It is asking locals to try something else on their country's big day: Make love for Singapore.

The soulful rap, which is part of a new ad campaign to promote Mentos mints, is called 'National Night,' and it exhorts Singaporeans to 'do their civic duty' to help solve the city-state's low birthrate by making a baby on Aug. 9.

'It's National Night, let's make Singapore's birthrate spike,' a female vocalist sings over jittery synthesizers and drumbeats, as her male counterpart shouts phrases like 'that's right' and 'the birthrate won't spike itself!'

'Singapore's population, it needs some increasin', so forget waving flags, August 9th we be freaking,' the rap continues.

The song has gone viral, taking on a life of its own on social networks across the famously staid city-state. It is also raising the eyebrows of older residents who fret that it is mocking a serious issue.

Singapore's leaders have worried for years about the country's birthrate, which is among the lowest in the world at 7.72 births per 1,000 people, according to 2011 estimates from the CIA World Factbook. That means the country's population would keep falling every year if authorities didn't let in immigrants - a policy that doesn't go down well with many locals, who say they resent new arrivals who take jobs and strain local resources.

The government has tried just about everything to get the birthrate back up. It has offered 'baby bonus' tax breaks and government-paid maternity leaves to new mothers. It has also set up a special government unit, the Social Development Unit (SDU), now renamed the Social Development Network, to help singles meet and mingle. Thanks to the unit, locals can sow the seeds of romance at government-subsidized speed dating events and salsa dance classes.

Over the past year, the government has designed a series of instructional comics, including one exploring different 'love fallacies' that singles often have. In one of the strips, a young woman tells her friend she is waiting for the 'right one' to come along, only to find a 100-year-old man, lonely and wrinkled, as the only one who agrees with her. The comic comes with this advice: '[A relationship] is a matter of going out of your comfort zone to meet new people. . .and not being afraid to love and commit.'

National Day, which includes giant parades presided over by Singapore's top leaders and lots of military displays, has become a prime forum for messages about making babies. At the 2008 National Day, for instance, Prime Minister Lee Hsien Loong spent more than 5,000 words discussing Singapore's falling birthrate. The speech included advice on how to change diapers.

'In the days before Pampers, you actually got to fold the cloth, you got to put it on, you got to put the safety pin in and I haven't pricked any baby yet,' Mr. Lee told a rapt nation. 'If I can do it, it means everybody can do it.'

All that talk of making babies does seem to be having some impact. In 2003, according to surveys by condom maker Durex, Singapore was among the bottom three nations in the world when it came to frequency of having sex. Five years later, more Singaporeans were having sex at least once a week than Australians, Americans, British and Canadians, according to a similar survey by Durex.

But the birthrate has continued to decline steadily, although with a slight improvement in the number of babies born last year, according to government statistics.

Enter the Mentos campaign, which was composed independently of the government as a parody of officially sanctioned National Day songs that play in the months leading up to Aug. 9 each year, and are sung during National Day parades.

There is a new official song each year. This year, it is called 'Love at First Light,' and comes with a music video highlighting Singapore's newest attractions, like a new billion-dollar public park called Gardens by the Bay. It also celebrates Singapore's 'lively ways' and 'warm sunny days.'

The Mentos rap has other ideas.

'Let's not watch fireworks, let's make 'em instead,' the rap's male vocalist croons. 'It's National Night and I want a baby, boo, I know you want it, so does the SDU.'

The song, devised by ad agency BBH Asia-Pacific and spread via social media, is part of Mentos's plan to launch a special 'I Heart SG' pack of their signature mints for this year's National Day. The agency was asked to come up with a campaign to 'prove how much Mentos really 'hearts' ' Singapore, according to the project's creative director, Adrian Chan.

'Mentos has always stood for 'fresh thinking,' so we decided to apply some to an issue that is very close to home: our declining national birthrate,' said Mr. Chan.

In one part of the song, one of the singers advises, 'come on now, let's get that baby bonus.' And in case any locals might be offended, a singer says listeners should just get over it and, 'well, get [their] National Night on.'

Some Singaporeans were tut-tutting as the song went viral.

'The clip should not be shown during the National Day Parade season. . .you do not want to trivialize the baby issue,' said Lee Chun Wah, a professor at the Nanyang Technological University in Singapore specializing in brand communication.

'The conservative folks - the traditional 'heartlanders' - may be offended,' he said, adding that he personally finds the song 'hilarious.'

Mr. Chan said he hopes the government will like it, given the importance and urgency of the issue of fertility in the city-state. Officials contacted about the song and its video said only that Singapore's government wasn't involved.

The video does come with an important disclaimer. Only 'financially secure adults in stable, committed, long-term relationships should participate,' it advises.