The National Stadium may have a capacity of 55,000 but it took less than four hours for tickets to K-pop boy band BTS' concert to sell out after they went on sale yesterday.

Sales started at 10am, and at 1.30pm, concert organiser One Production announced on its Facebook and Twitter accounts that the Jan 19 show was sold out.

Some fans had started queueing five days before tickets, priced from $88 to $348, went on sale at the box-office booths outside Kallang Wave Mall.

Malaysian Melody Siow from Kuala Lumpur managed to secure two tickets. The personal assistant in her 30s accessed the Sports Hub ticket website about an hour before ticket sales started.

"I'm very excited and happy, I can't wait," said Ms Siow, who bought a pair of $268 tickets for herself and her sister.

Many were left disappointed. One of them was housewife Sophia Phang, 36, an American based in Petaling Jaya, Malaysia.

She said she was in the virtual waiting room of the Sports Hub ticket website from 2am yesterday. Her husband was also trying to get tickets on his laptop, she said.

"For sure I'm disappointed," said the K-pop fan of 20 years, adding that she will try to get tickets for the Thailand and Hong Kong concerts instead. BTS will be performing in Hong Kong and Bangkok in March and April, respectively, as part of its Love Yourself World Tour.

Yesterday morning, The Sunday Times found more than 20 postings on online retail platform Carousell that claimed to sell tickets for the BTS concert here. Many were charging commissions of at least $50 for each ticket.

BTS, which has seven members aged between 21 and 25, last held a concert here in 2014. The band made its debut in 2013.

Recently, it gained massive success as the only K-pop entrant to top the Billboard 200 albums chart.

It also made the cover of Time magazine's latest edition, and the band members gave a speech at the United Nations last month.