Four years ago, when Dr Liu Thai Ker said Singapore should plan for a population of 10 million to remain sustainable as a country, it raised eyebrows.

Yesterday, the former chief executive of the Housing Board stood by his comments yesterday in an interview with The New Paper at the Sands Expo and Convention Centre on the first day of the PropertyGuru Asia Real Estate Summit.

Dr Liu, 79, who has been dubbed the architect of modern Singapore, said it was important to start planning now for Singapore to remain relevant as a country.

He led HDB from 1979 to 1989. He then became chief planner and chief executive of the Urban Redevelopment Authority until 1992. Dr Liu is now the senior director of RSP Architects Planners & Engineers.

He said planning without calculating the land resources available to support population growth could put us at risk of running out of land.

Dr Liu, who is also founding chairman of the Centre for Liveable Cities, added: "Before Singaporeans complain, they have to ask themselves: How long do you want Singapore to stay as a sovereign country?"

He said it would be difficult for the country to depend on neighbours should the need arise.

Referring to a White Paper released in 2013 that projected Singapore's population to hit 6.5 million to 6.9 million by 2030, Dr Liu suggested in a forum later that year that Singapore could look ahead to a population of 10 million people by 2100.

Netizens criticised his comments, with many worried Singapore's infrastructure could not support such a large population.

Dr Liu said his idea of the population increasing from the current 5.6 million to 10 million in less than a hundred years was a low estimate of the growth rate.

While the Government has been taking steps to curb population growth, he said: "You cannot stop population growth, because as long as your economy is booming and you create new jobs, you need new population."

Over the past year, Singapore's population grew by just 0.1 per cent, the National Population and Talent Division said in September.

Dr Liu added that if he was still in urban planning, he would create two or three major civic spaces in the downtown area, similar to Tiananmen Square in China and plazas in Paris.

Asked about the issues facing rail operator SMRT, he said that when it came to urban issues in general, it was human to let things slide a little.

He said: "The acid test of government is when you notice this happening, do you do something to address it? I think our Government is doing that."