Kim Jong-hyun, the lead singer of popular South Korean boy band SHINee, was found dead Monday in Seoul. He was 27.

Kim, better known by his stage name Jonghyun, was found unconscious at a residence hotel and was pronounced dead later at a nearby hospital.

Police said Kim's sister told them that, before his death, the singer had behaved erratically and sent her text messages that included messages such as "Final farewell" and "I've had difficulties."

The members of SHINee pose with New York fan Donika Sterling, bottom centre, in Seoul in 2012. (Lee Jin-man/Associated Press)

Yonhap news agency said authorities found burned coal briquettes, which produce carbon monoxide, in a frying pan in Kim's hotel room.

Police said they have not yet determined whether he killed himself.

Kim debuted in 2008 as the main singer of SHINee, and cultivated a career as both a group member and a solo singer-songwriter. His last public appearance was at a solo concert titled Inspired on Dec. 9 and 10 in Seoul.

He was scheduled to hold concerts with SHINee members in Tokyo and Osaka in February, Yonhap reported.

"Fans from all over the world of every K-Pop group have come together to remember the positive ray of light that was Jonghyun," Gerald Belanger, CEO of Toronto K-Pop Con organizing firm Pop! Goes the World, told CBC News in a statement Monday afternoon.

"He will be sadly missed. Our whole team is speechless and many are in tears today."

SHINee is one of the K-Pop acts Canadian devotees treasure because the group had travelled to Canada twice in the past two years to perform live, Belanger noted.

The members of SHINee pose at a press conference in 2014 in Seoul. (Starnews/AFP/Getty Images)

South Korea has one of the highest suicide rates among developed countries. A string of high-profile figures, including a former president and business executives, have killed themselves in recent years.