When Prime Minister Lee Hsien Loong decided to field Mr Murali Pillai as the People's Action Party candidate in the Bukit Batok by-election in May, he knew it would not be easy for a non-Chinese candidate to win.

But Mr Murali, who faced Singapore Democratic Party chief Chee Soon Juan, won with 61.2 per cent of the votes.

Speaking in Parliament yesterday, Mr Lee said: "He fought hard, he won, but he can tell you, and I can tell you, that he had to fight harder than if I had sent a similar Chinese candidate familiar with the ground to go and fight and win."

"It is a reality of Singapore society and Singapore politics," he said, making the point that minority candidates face an uphill battle.

This is why it is crucial to make arrangements to ensure the presidency remains multi-racial, he added.

One of the proposed changes to the elected presidency being debated this week seeks to reserve elections for candidates from particular racial groups if they have not been elected into the office for five continuous terms.

Referring to a Channel NewsAsia-Institute of Policy Studies survey on race relations, Mr Lee said a significant minority of Singaporeans consider race as a factor when they vote, and will not vote for somebody of a different race to be president.

He added: "Not everybody, but not a small minority either. And that puts the minority candidates at a disadvantage in an election. "

"If we do not make deliberate arrangements to ensure a multiracial outcome, the presidency could well become a single-race office because minorities do find it harder to win in a national election."

Mr Lee acknowledged that this is not an easy subject to speak about openly, as many people feel they are race-blind and are uneasy about any suggestion that they may not be so.

"I am heartened that is our ideal and aspiration but, at the same time, we have to be realistic about where we are today," he said.

Charissa Yong