For BTS ARMY members, as the K-pop phenomenon's fan base is known, the timing of Jin's discharge from South Korean military service couldn't have been more fortuitous.

Just 24 hours after the oldest member of the world's biggest boyband was discharged from duty, the South Korean capital was overtaken by BTS fans, with tens of thousands of people lining up Thursday to join the group's annual party.

Organised by HYBE, the band's agency, the BTS FESTA last year saw 400,000 fans attend.

This year's event, held at a sprawling sports complex in southern Seoul, is expected to exceed the record, with Jin giving out free hugs at a nearby location to a select group of 1,000 lucky raffle winners in a "huggathon".

With lines stretching up to three kilometres around the FESTA venue, fans showed up from as early as 7:00 am to make sure they could get their hands on the band's coveted merchandise and free photo cards of their idols.

BTS has been on a self-described "hiatus" since 2022, with all seven members conscripted successively for military service.

Due to tensions with the nuclear-armed North, South Korea requires all men under 30 to sign up for service.

After his discharge on Wednesday, Jin said on South Korean app Weverse that the "huggathon" was his idea, and that he had "initially wanted to hug 3,000 fans" but that he had to agree to a smaller number due to safety concerns.

As she waited for the annual party to kick off, BTS fan Lisa Pavelchack said she was really proud of Jin "for doing what he needed to do" in life.

The 48-year-old from Ohio said she had flown to Seoul especially for the FESTA, which she was attending with friends she had met at a BTS concert in the United States.

Ann Suwanan, a 19-year-old from Thailand, was sad that she, like Pavelchack, was not going to get the chance to hug Jin.

"I wanted to hug him so much," she told AFP.

Wearing a purple tulle dress and a big purple bow in her hair, she said she "cried a bit" with joy when Jin was discharged.

Hector Sosa, a 40-year-old father, said he had flown from Mexico to Seoul to accompany his adoring ARMY member daughter.

"My daughter is a fan of theirs and we came for her birthday as a present," he said.

"We landed at 5:00 am today in South Korea and came straight here."