New York (AFP) - Ten years ago, most vinyl records sold for a few dollars -- dusty old albums with dog-eared covers that had been thrown out as useless relics of an earlier age.

However, faced with twin onslaughts from digital music and big-box stores, independent record stores in the United States banded together in 2007 to create an annual day of special sales -- and much to their surprise, vinyl has been king.

Metallica played the first Record Store Day at a branch of Rasputin Music in the San Francisco area. While the metal legends' presence ensured a crowd, all 10,000 vinyl reissues at the store sold out that day.

"That made me realize we were onto something. We tapped into something that nobody could have imagined," Record Store Day co-founder Michael Kurtz said.

Kurtz quickly expanded Record Store Day to continental Europe and Britain, where the first British edition was championed by Billy Bragg, the folk rocker known for his left-wing activism.

The 10th annual event takes place Saturday at thousands of stores around the world -- due to the deliberately loose structure, Kurtz does not have an exact figure -- with some 350 special vinyl pressings in the US market released on the day.

Since the first Record Store Day, vinyl has soared to levels not seen since the 1980s. It has been a rare source of growth in the long-beleaguered music industry alongside -- although at a much smaller scale than -- streaming.

Vinyl revenue will top $1 billion this year while sales of CDs and digital downloads tumble, the analytical firm Deloitte estimates.

In Britain, where vinyl's rebirth has been particularly pronounced, records generated more revenue than advertising-backed tiers of streaming platforms last year.

- Owning a format -

Vinyl enthusiasts such as Elton John, who has done promotions for Record Store Day, insist the medium offers a superior listening experience. But there are also broader cultural forces at play.

"It was a perfect storm," said Kurtz, 59, sipping coffee near his home in Harlem as he wore a T-shirt of punk icon Iggy Pop -- among the musicians with special Record Store Day releases.

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"For the older music fan, people in my age group, it was a romantic thing that you can go back and buy all your favorite records again and buy special versions of those albums," he said.

"On the younger side of things, it enabled a whole new generation to own it. I think it was a response to digital in a way."

In a sun-kissed industrial plaza in Orange County, California, Erika Records never stopped making vinyl. But production has ramped up eight times in the past decade. The plant now produces 20,000 records a day.

"The vinyl resurgence has been very good to us," project manager Ma Nerriza dela Cerna said next to the plant, where records by artists from Lady Gaga to Bob Marley are manufactured from start to finish.

Part of vinyl's draw is the unique touches it provides for fans. Erika Records, the sole US plant to make color and picture records, works with artists to create original designs -- although it drew the line when one band proposed infusing its members' blood into the vinyl.

- Will boom last? -

"A lot of people say that the vinyl industry will eventually slow down," dela Cerna said. "I personally don't think that only because I feel like we're introducing vinyl to a new audience every day."

Record Store Day and Erika Records both have their roots in working with independent labels, although major conglomerates have since joined the event.

Unlike some indie purists, Kurtz rejoices in major labels' participation as a signal of vinyl's success. But he also worries that the same trends that battered independent stores a decade ago are coming back, with some labels bypassing them to sell directly to consumers.

Vinyl's growth has also been inconsistent. A major format for indie and classic rock and jazz, it has had much less impact in hip-hop, where top artists often find it more lucrative to sign streaming deals.

While vinyl makes up an ever-greater part of the market, the rate of growth in the United States slowed to four percent in 2016.

Kurtz isn't worried. Record store owners are enjoying themselves, he said, and the expansion was expected to plateau.

"Music has always had a core 10-15 percent of the population that buys the full vision of the artist, whether it's on CD or vinyl. And right now it's pretty close to that."