Singaporeans living in the United Kingdom were among the first to cast their votes.
The Singapore High Commission opened its doors at 8am (Singapore time 3pm) on Thursday, but a queue with seven people had already formed 15 minutes earlier at the building near Knightsbridge in London.
Most who arrived early made it their first stop before going to work.
Public servant Samuel Chang, 31, and his wife Gerlynn Ho, 27, were at the mission's door at 7.30am as they were driving to Cornwall for a holiday later. Both were voting overseas for the first time, after they moved to London two months ago for Mr Chang's work.
Most in the queue were young, first-time voters who said they kept themselves informed of the issues during the election campaign through social media.
Student Rhea Tan, 24, found this election more exciting than the 2011 polls. "All the seats are being contested, unlike in the past, when you may not have a say."
Trainee solicitor Koh Yi Na, 23, said interest among the young was high."We are starting to vote at a time when there is genuine choice given to us and there is a sense of there being an opposition.
"That's why we need to and are making more of an effort to choose what we want," she said.
Ms Amandas Ong, 24, a marketing coordinator in a financial consultancy, said she thought "very long and hard" about which party to vote for in her Ang Mo Kio GRC.
London is one of 10 overseas polling stations, which are in places with a significant number of Singaporeans. The rest are in Dubai, Washington, New York, San Francisco, Tokyo, Beijing, Shanghai, Hong Kong and Canberra. But the polling stations that opened a day ahead of Singapore are those in London, Dubai, New York, Washington, DC, and San Francisco.
In Washington, the polls also opened at 8am (8pm Singapore time) and Mr Leow Wei Jen, 50, a Marine Parade GRC voter, was the first through the door at the Singapore Embassy.
He has been living in the United States for 17 years, but "it's important to vote because I'm Singaporean", he said. He followed the electoral news online, he added.
The polls also opened at 8am (8pm in Singapore) in New York City and at 8am (11pm) in San Francisco on the west coast.
Like in London, many of the early voters in Washington arrived in office attire, ready to head off to work after casting their ballots.
First-time voter Joy Sim, 24, said she was concerned about issues such as housing, cost of living and her parents' retirement.
The consultant, who has been living in the US for five years and is a voter in Chua Chu Kang GRC, said it was good to see opposition teams "starting to build their base".
"But there is a lot more for the opposition to do in the western part of Singapore," she added.
A Tanjong Pagar voter, who wanted to be known only as Mr Yeo, flew from Chicago to cast his ballot in Washington.
The 50-year-old said it was the first time he was voting since 1991 and he was happy to be able "to exercise the rights of a citizen" this year. "Having no contest all these years was almost as if we didn't have that right. It's good there is competition. I see voting as a serious responsibility," he said.