The marathon category of the Standard Chartered Singapore Marathon (SCSM) has sold out for the first time in its 16-year history, affirming its reputation as the top premier running event in Singapore.

Registration officially closed on Wednesday with more than 12,500 signed up to run the 42.195km marathon on Dec 3, a 20 per cent increase from last year.

Said Geoff Meyer, managing director of organisers Ironman Asia: "These numbers show the SCSM is one of the most attractive races in the region, and we're working towards delivering a top-class experience for everyone at the race this year."

Attracting just 6,000 runners in its first edition in 2002, the SCSM will have about 50,000 this year across its five categories.

The Ekiden category, which sees teams of six runners take turns to complete the marathon distance in a relay concept, has sold out as well. The half-marathon and 10km categories have fewer than 200 and 400 slots remaining respectively, while there are around 800 Kids Dash spots left.

The SCSM has become synonymous with distance running in Singapore, said Deloitte Singapore and South-east Asia sport business group leader James Walton.

"When you think about marathons in Singapore, when you talk to people about their first marathon runs, invariably it's the SCSM that comes up," said Walton, a marathon runner himself.

"Part of the reason is that while we're seeing more 10km types of events, there really isn't much to compare (to SCSM) at the marathon level. For people who really want to test themselves, the SCSM stands out as one with a good reputation for being professionally organised."

National runner Fang Jian Yong, who competed in the 2015 SEA Games, said the SCSM has done well to market itself locally and regionally. "Everyone knows about (the SCSM), even non-runners. It's called the Singapore Marathon for a reason," he said.

"It's the biggest event here and also attracts a lot of foreigners."

For this year's marathon, 48 per cent of the entrants are non-Singaporeans, including expatriates living here as well as tourists.

The SCSM is bidding to join the Abbott World Marathon Majors this year but one factor that might hamper its efforts is Singapore's heat and humidity.

"A lot of racers want to run a race where they can run a good time but Singapore is not a place where you can run a personal best," said Walton .

Added Fang: "The biggest concern is still temperature. Perhaps more attention could be paid to hydration, like spreading the water points a little closer."

• Registration is still open. Sign up at singaporemarathon.com