As of now Singapore's demographics may not have become a major issue -- but it will be in a generation's time, on a 25-year timeframe.
The immediate challenge over the next decade is getting the economy to the next level, Lee said in an interview published today by Time magazine.
"We are looking for a path which no country has yet found and we are not even an economy like the Japanese or Germans, or never mind the big power economy.
Lee said enhancing the economy, the ageing population and maintaining a national identity are three "biggest challenges" Singapore faces over the next half-century.
If Singapore does not get the balance between birthrate and immigration policies right, it could end up in the same "tight spot" the Japanese currently face, Lee said.
Japan fears that by 2060, nearly 40 per cent of the population will be aged 65 or over. Government data released in April showed Japan's population slid for a third year with the proportion of people over the age of 65 at global record.
"The solution we have to be able to work, is to have enough of our own children for the next generation," Lee said in the interview reproduced by Channel News Asia.
Responding to Time magazine's observation that Singapore has been "quite successful" in forging a national identity, Lee said the issue was "not that simple."
He highlighted sub-divisions such as race, language, religion, as well as personal positions on lesbian, gay, bisexual and transgender -- issues that could cause tension.
"If you don't have that Singapore core, you can top up the numbers, but you are no longer Singapore. It doesn't feel Singapore, it isn't Singapore and we can issue everybody red passports, but where is the continuity?" he asked.
"And keeping that sense of unity and specialness over the long-term -- I think it is critical and it is a very big challenge," he said.
Asked if Singapore with its majority-Chinese population could one day have a non-Chinese prime minister, Lee said it depends on the candidate.
"You must have the right person -- you must have the politics worked out, you must be able (to) connect both with the Chinese as well as the non-Chinese population.
