Again raising the niggling issue of a declining birth rate, the senior minister said the city-state needed a hard core of native Singaporeans.

With a fertility rate of less than 1.5 children per woman, well below the 2.15 necessary for a population to replace itself, Lee said immigration can make up the loss "but natural replacement is better."

"Our educated should have three children per family," media reports on Wednesday quoted Lee as saying.

"In this way we can keep strong that core of native-born Singaporeans.

"They will keep Singapore going through thick and thin, and never give up no matter how difficult the problems."

While immigrants can come to Singapore to work "as experts," it was native Singaporeans "who will stay and fight and win," he said.

Singapore's reliance on immigration to keep the population steady has seen the number of non-Singaporeans swell from 14 percent to 25 percent of the four-million population in the past decade.

Native Singaporeans, relishing the benefits from the republic's rapid rise from backwater to economic powerhouse, are opting to put career and money ahead of family.

The government has set up an inter-ministry committee to draw up a strategy to boost the birth-rate.

Incentives unveiled so far include the payment of a "baby bonus" to parents, building more university hostels to draw students together, and flexible working hours so civil servants can spend more "quality time" at home.