Seoul,  The K-pop album market has been experiencing an unprecedented boom, but the sales of digital music have been sluggish amid the coronavirus pandemic, reports Yonhap News Agency.

According to the year-end data released by Korea's album sales tracker Gaon Chart, the nation's top 400 albums sold 57 million copies in and out of the country in 2021, up by 36.9 per cent from 41.7 million in the previous year.

The sales of the top 400 albums have been on a steep rise after exceeding 20 million for the first time in 2018. The number has since increased to 25 million in 2019, 41.7 million in 2020 and 57 million in 2021.

Industry insiders say that behind the rapid increase since the coronavirus pandemic began in 2020 is the phenomenon that fans, unable to gather at live concerts and shows amid the protracted pandemic, soothe their disappointment by purchasing albums.

Leading the album market last year were South Korea's big two K-pop agencies -- Hybe and SM Entertainment.

Hybe, behind popular boy groups such as BTS and Seventeen, accounted for 33.5 per cent of the total sales of the top 100 albums on Gaon's annual chart, with combined sales of 26 albums by its artistes on the list reaching 15.23 million copies.

'Butter', the English single released by BTS in May, sat atop the list with about 3 million copies, and other Hybe artistes, such as Seventeen, Tomorrow X Together and Enhypen, also produced remarkable performances.