Fans are pouring into the historic heart of South Korea's capital for what may well be the year's biggest event: the return of the world's most successful band in recent years, BTS.

Some 260,000 people are expected to turn up on Saturday at Gwanghwamun Square, where the seven K-pop stars - RM, Jin, Suga, J-Hope, Jimin, V and Jung Kook - will perform together for the first time since October 2022.

Set against the backdrop of a 14th Century gateway to the royal palace, the band's one-hour set will include songs from their long-awaited new album, Arirang, which was released on Friday afternoon.

For South Korea, this is more than the comeback of a K-pop band - it's also the return of a cultural force that has propelled Korean soft power with its record-busting mix of punchy pop and electric dance moves.

How do we watch the BTS concert?

Only about 22,000 people who managed to get free tickets will enter the concert venue - a smaller area in Gwanghwamun Square that has been cordoned off.

Ami Ostrovskaia, who moved to Seoul from Russia last year to study, is one of the lucky ones. "BTS is the reason I'm here," she says. "It's why I started learning about Korean history, culture, food, sports, and the language."

The rest will watch the giant screens outside: like Margarita Perez, a 58-year-old architect from Germany. She didn't manage to snag a ticket but has been scouting the area so she can "stay nearby" on concert day.

Jacqueline, a 29-year-old teacher from Mexico City, will also be at Gwanghwamun Square on Saturday to catch a glimpse of her favourite stars, before she sees them next month on the world tour.

"The last few years have been a sad time for [the BTS] Army. I loved their solo albums, but they're more amazing when they're together."

As for the millions of fans around the world, the concert will be live-streamed on Netflix.

As part of its deal with BTS, Netflix has exclusive rights to live-stream the show, as well as a documentary on the band's reunion - a marketing triumph given the billions it has pumped into Korean entertainment.

What do we know about Arirang, the new BTS album?

The album's title, Arirang, is the name of Korea's most beloved folk song, a sentimental anthem about moving from hardship towards something better.

It is not lost on the band that the first known recording of Arirang was made in the United States in 1896, performed by a group of seven Korean men at Howard University.

A promotional video for the album shows RM, V, Jin, Jungkook, Jimin, j-hope and Suga listening to that wax cylinder recording, spinning a narrative that puts them in the same bracket - exporting Korean culture to the world - but 130 years later.

On Saturday, the band's music label, Bit Hit Music, announced that Arirang had sold 3.98 million copies on the first day of its release.

The album - and Saturday's comeback concert - is a culmination of years of anticipation since BTS went on hiatus in 2022, at the peak of their fame.

They did so to enlist for mandatory military service, starting with Jin in 2022. Suga was the last to complete service in June last year, paving the way for a full-group comeback.

Their 82-date world tour across more than 30 cities, from Singapore and Tokyo to Munich and Los Angeles, begins next month.

The stakes are high as BTS returns to a K-pop industry that has got bigger and more competitive.

"They've always exceeded my expectations. They might feel the pressure, but I believe they'll do their best," says Park Joo-young, a student in her 20s, who has been waiting a long time for this.

How has Seoul prepared for the BTS concert?

Authorities are pulling out all the stops.

As landmarks light up in the band's signature shade of purple, some 7,000 police officers - including SWAT units equipped with anti-drone systems - will be deployed to manage the crowds at the square.

As the capital's central district turns into a massive, open-air stadium for BTS, access to dozens of buildings will be restricted and three subway stations nearby will close.

In the hours before and after the concert, access to the square - a popular, open space - will be controlled through 31 entry points fitted with metal detectors.

Although South Korea has strict gun control laws and private ownership is rare - with firearms typically stored at police stations - authorities will temporarily bar civilians from retrieving them.

And as BTS puts Seoul on high alert, local businesss are buzzing with excitement for the rush of tourists drawn here by their love for the boy band.

Before BTS went on hiatus, the Korea Culture & Tourism Institute estimated that a single performance by the group could generate up to $842m (£621m) - including ticket and merchandise sales, accommodation, tourism and other related spending.

And when this tour wraps up in 2027, BTS are expected to have generated more than $1bn in revenue.

Hotels around the area were fully booked or had begun raising prices more than a month ahead.

"I'm preparing menus in English, Chinese and Japanese, and decorating the restaurant with purple flowers," Kim Sung-dae, owner of a nearby seafood restaurant said, in reference to BTS's signature colour.

What are South Koreans saying?

With most of Gwanghwamun Square blocked, forcing pedestrians to take long detours, many nearby events that had been planned well in advance were thrown into uncertainty by the BTS concert.

This was a particular source of stress for Sohn Yeon-ju, a lawyer in her 30s, who was supposed to hold her wedding near Gwanghwamun Square just hours before the concert.

By Thursday, it was still unclear how she and her hundreds of guests could make their way to the heavily guarded venue. Police told her that guests might be allowed to board police buses if the nearest subway station was closed.

A Seoul city official told the BBC that authorities had provided the BTS concert with the venue, crowd management and other safety measures - but not direct financial support.

But some in South Korea were still torn about whether authorities had focused too much energy on the concert.

"They've pulled in police and fire personnel en masse. If something happens elsewhere, there may be no staff left to respond, and access could be blocked because of the controls," one user wrote on X.

In another post on X, pop music critic Jung Min-jae said: "If a comeback concert of this scale, one that effectively paralyses parts of the city centre, is allowed, then other artists or agencies may well request to use the same space in the future.

"At that point, on what criteria will the Seoul Metropolitan Government approve or reject such requests?"

But some see these inconveniences as a small price to pay for the popularity that BTS has brought the country.

"I don't see what the problem is," wrote one local who lives close by.

"BTS has done so much for Korea, elevating our image abroad, with no government support all along. Why can't we share the Gwanghwamun public space for their performance just one Saturday?"

What do BTS fans think?

The BTS Army, as the band's millions of fans call themselves, have fought hard to get the tickets for the concert on Saturday.

Some 13,000 free tickets were snapped up instantly when reservations opened last month, a fraction given that more than 100,000 people had been queuing online. Another 7,000 free tickets were released later, and also sold out within minutes.

"I tried with both my smartphone and a desktop computer - none of them worked," says Rachel, who doesn't describe herself as a BTS fan but "they're so talented and globally famous that I wanted to take this chance to see them perform live".

The free tickets have upset some who say it reduces the chances of dedicated BTS fans securing tickets. Fans have even launched campaigns to discourage resales and prevent "no-shows".

And others are unnerved by the massive crowds swarming to Gwanghwamun Square.

"I know officials will strengthen safety measures, but there will be so many people that I'm still a bit worried," says Park Su-bin, a wheelchair user in her 30s.

She has tickets for the group's concert in April, so she decided to skip the Gwanghwamun event.

Ami Ostrovskaia initially failed to get a ticket - "I was crying the whole night" - but, thanks to a friend, the 23-year-old got lucky.

"I was so happy and felt like all my problems were gone. This means that I'll be joining their [full-group] performance after so many years. It's really meaningful for me." (BBC)

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