The polls were kept open for two more hours last night till 10pm so that voters caught in long queues at a number of polling stations could cast their votes.

The Elections Department (ELD) announced the extension - believed to be the first time this has happened - at around 7pm. It noted that although the queue situation across most stations had improved, "a small number" continued to see long queues.

ELD had earlier apologised for "longer than usual" queues at polling stations during the day, and attributed these to a combination of voters turning up to vote outside their assigned time bands, as well as measures put in place to ensure safe voting during the pandemic.

Opposition parties criticised the move to extend polling hours.

Progress Singapore Party (PSP) chief Tan Cheng Bock said the move was "highly irregular"and "compromised the integrity of the process".

"This is a direct result of bad planning and incessant urge to rush an election during the (Covid-19) period. This underscores the disregard for public health, as well as our democratic processes," Dr Tan said.

He added that after studying the Parliamentary Elections Act, his party is of the view that the Returning Officer has no power to extend polling hours, especially on the day itself after polling starts.

A notice of the extension of polling hours was published on the government gazette at 7.10pm.

The Singapore Democratic Party (SDP) called the extension "highly irregular" and unprecedented.

Meanwhile, Singapore People's Party (SPP) secretary-general Steve Chia expressed concern that the extension coincided with the special voting hour for those who are unwell or on stay-home notice.

He added that SPP had told its polling agents to stay away from the centres, and return after the close of voting at 10pm to witness the sealing of the ballot boxes.

A special voting hour of 7pm to 8pm had initially been set aside for those on stay-home notice, on medical leave due to acute respiratory infection, or who had a fever, to cast their votes.

ELD said that in view of the extended hours, election officials would ask such voters at stations that still had long queues to identify themselves.

These voters would be isolated in a separate holding area, in order to prevent them from mixing with other voters. Once the queue had cleared, election officials would then arrange for them to vote.

ELD also said that the extended hours - which did not apply to stations in designated stay-home notice facilities - did not affect polling and counting procedures.

It added that parties and candidates could continue to exercise their rights and obligations in ensuring a fair and open election, including witnessing the sealing of ballot boxes and observing the counting process.

Voter Raymond Francis, 50, called the extended voting hours "a godsend". He and his wife were originally given the time band of 4pm to 6pm to vote at Newton, but saw a line of more than a hundred people when they got there at 4pm.

"We felt it was quite crowded and didn't want to queue under such conditions under the heat, and we were worried about social distancing as well," he said.

After hearing about the extended voting hours, they decided to come back only at 8.15pm. Conditions then were much better, he said.

Over at Palm View Primary School, Madam Lim Swee Geok, 54, voted at 8.30pm. She had tried to vote three times earlier in the day - at 11am, 5pm and 6.30pm - when queues were long, with more than 200 estimated to be in line.

Madam Lim said the extended voting hours were good, but that the earlier queues were "very long" and she had gone home instead of waiting as she had not been feeling well.

"I almost didn't want to vote - this is the first time that voting has been so difficult and so tiring," said the Sengkang GRC resident.

Political scientist Bilveer Singh said that while the extension may have been unprecedented, it was the right thing to do.

"Rather than cutting it off and stopping people from voting, which will be more damaging, I'd rather extend it so that everyone is able to cast their vote and then we deal with whatever the consequences after that. I think what's most important is that everybody's voice needs to be heard," he said.

• Additional reporting by Fabian Koh, Tee Zhuo, Ling Chang Hong and Kok Yufeng