An ageing and shrinking population could mean higher taxes on those working to fund subsidised healthcare for a large number of seniors, Deputy Prime Minister Teo Chee Hean said on Monday.

Stressing that the problem of an ageing society needs urgent attention, he cautioned that business activity could slow down with less investment in new sectors, and fewer job and career opportunities.

He said that the maintaining a sustainable and stable Singaporean population was thus the "first and most important part" of the Population White Paper.

"Young Singaporeans may decide to leave for more exciting opportunities in other growing cities. This would hollow out our population and workforce. This is a real worry for parents too who wonder whether their children will go abroad in search of better opportunities, and they will be left alone here during their silver years," he told Parliament when opening the debate on the Government's Population White Paper.

He noted that between now and 2030, over 900,000 Baby Boomers - or more than a quarter of the current citizen population - will enter their silver years. By 2025, the citizen population will start to shrink if nothing is done.

At a total fertility rate of 1.2, for every 100 Singaporeans in this generation, there will be 60 Singaporeans in the next generation, and only 36 in the generation after that.

"This threatens the sustainability of our Singaporean core population," he said.

The ratio of working-age citizens to each citizen aged 65 and above will also fall, from 5.9 now to 2.1 by 2030.

He said: "The issue is indeed upon us, and is an issue we need to deal with now."