Opposition candidate Png Eng Huat from the Workers' Party won by a landslide in a Singapore by-election as voters handed a stinging rebuke to the ruling People's Action Party in a poll seen as a referendum on their recent reforms.

The Workers’ Party retained the seat in the district of Hougang, winning 62.09% of votes cast despite having to fire the previous member of parliament over allegations of extramarital affairs.

The ruling People’s Action Party (PAP) got 37.91%, the elections department said.

Prime Minister Lee Hsien Loong and other PAP big guns had gone all out to campaign for the ruling party candidate, Desmond Choo, but in the end failed to win control of the ward, which has been in opposition hands for the past 21 years.

The vote took place a year after the ruling party, which has been in power more than half a century, suffered its worst performance in a general election.