The Bukit Batok by-election has not been called, but the two candidates who have said they will stand there are gearing up for a tough fight.

Over the weekend, People's Action Party candidate Murali Pillai and Singapore Democratic Party chief Chee Soon Juan, along with their teams, were out in full force, distributing fliers and greeting residents. The SDP also unveiled its campaign message on Saturday.

Deputy Prime Minister Tharman Shanmugaratnam said on the sidelines of a community event on Saturday that the People's Action Party was not taking anything for granted.

"Certainly we're not taking anything for granted. I think it'll be a tough fight in Bukit Batok, and we have a very good man who knows the ground well and is certainly going to work very hard," he was quoted as saying in Chinese-language daily Lianhe Zaobao. He added: "I think it will be a good contest."

After a walkabout yesterday, Dr Chee said his party had ramped up its activities to let residents know "we need to get into Parliament in order to speak up for them".

His party had said on Saturday that his campaign slogan, "Now is the time", conveys the importance of electing an alternative voice to Parliament.

"Adding one more People's Action Party MP to the existing 82 will not make any difference in any way," the SDP press release said.

Dr Chee, 53, said yesterday that he would speak about cost of living issues in Parliament and would also launch social programmes to help residents if elected.

The Bukit Batok seat became vacant after MP David Ong resigned on March 12 over an alleged affair.

Asked about the SDP's campaign message, Mr Murali, who has been a grassroots volunteer and leader in Bukit Batok for 16 years, said: "My priority at this time is to ensure that residents continue to be well taken care of, and that those in need get the help they require."

He contested in Aljunied GRC in last year's general election.

Dr Chee, who stood in Holland-Bukit Timah GRC in last year's election, said yesterday that he hoped to have a one-to-one contest with the PAP.

"Because anything else will dilute the opposition vote. This was our concern in the past, it still is our concern, but we cannot stop other parties from wanting to contest this ward," he said.

In last year's polls, Mr Ong won 73 per cent of the vote in a three-way fight against SDP man Sadasivam Veriyah, who got 26.4 per cent, and independent candidate Samir Salim Neji, who got just 0.6 per cent.

Prime Minister Lee Hsien Loong has said that he will call a by-election "in due course".

• Additional reporting by Lim Yan Liang