An estimated 300,000 people are expected to gather in the heart of South Korea's capital Seoul on Saturday as fans from around the globe commemorated the debut of K-Pop boy band juggernaut BTS 10 years ago.

BTS is on temporary break as a group with two of its seven members currently doing mandatory military service, but that didn't stop a host of celebratory events this week catering to the band's loyal fanbase known as "ARMY".

At the "BTS 10th Anniversary FESTA" at Han River Park in Seoul on Saturday, thousands of fans wandered under clear skies and bright sun among various exhibits including a BTS history wall, stage costumes and commemorative sculptures, many in BTS' signature purple colour.

With the bands' songs playing in the background, fans danced under shady trees or bonded over their favourite band members.

"Through this event I think we can get experience (of) how we build up our connection with BTS and ARMY," said Audrey Lintner, a 28-year-old master's degree student from Sri Lanka who was attending the event.

Later on Saturday, BTS leader RM is expected to speak to fans, followed by fireworks over the Han River, with local media estimating up to 300,000 people will be in attendance.

"Thank you so much for giving us great music and performances for the past 10 years," said Kim Hye-won, a 30-year-old who has been a fan since 2018.

"I'll continue to be an ARMY for 10, 20, 30 years, so I hope you as artists, singers, extend a lot of positive influence for a long, long time."