Punggol East residents should pick the PAP candidate to make the Workers' Party (WP) work harder for them, Education Minister Heng Swee Keat said on Sunday morning as he sought to use the opposition party's argument against itself.

WP chief Low Thia Khiang, in an election rally on Saturday, said the Government would work harder for residents if more opposition were voted into Parliament.

Mr Heng said on Sunday: "If that's the case, voters should look at what various MPs have done, contributed in their constituencies and in Parliament, then they'll come to the conclusion they should vote for the PAP to make the WP work harder for you."

The Government is working hard as it wants to serve people, Mr Heng added.

For example, it has invested in the education system for years even when there was no opposition in Parliament.

Speaking at a temple event in Tampines, he added that it is important to understand what the by-election is about, as he sought to keep the focus on local rather than national issues.

"This... is not about voting more opposition into Parliament, it's about electing the right candidate who can best serve residents of Punggol East," he said.

"Voters should cast their votes based on who is the best person who can serve them, and not for them to serve the interests of the opposition party."