SEOUL - K-pop group SHINee member Kim Jong Hyun, 27, died on Monday (Dec 18) in an apparent suicide, according to local reports.

Police found him unconscious at 6.10pm Korea time in his own apartment located in Cheongdam-dong, in the upscale Gangnam district, after his sister made a report at 4.42pm saying that her brother seemed suicidal.

The YTN news channel, however, reported that Mr Kim had checked into a serviced residence for two nights.

Mr Kim was taken to a nearby hospital, but eventually died.

Reports suggested he died of cardiac arrest from suspected carbon monoxide poisoning.

He was found to have burned a coal briquette on a frying pan. Charcoal briquettes can cause carbon monoxide poisoning in closed rooms.

Police are investigating the incident as a suspected suicide.

Mr Kim made his debut in 2008 as part of the five-member group SHINee, which produced hit singles such as Ring Ding Dong. He went solo in 2015 and just performed two solo concerts in Seoul last week.

He was also expected to appear on South Korean broadcaster JTBC's "Night Goblin" television show which was to air on Sunday.

According to the reports, his final message to his sister was: "It's been too hard. Please send me off. Tell everyone I've had a hard time. This is my last goodbye."

SM Entertainment issued a statement on his death on Monday night.

It said: "We're sorry to deliver such heart-aching, unfortunate news. On December 18, SHINee member Jonghyun left our side unexpectedly."

SM Entertainment called Mr Kim "the best artist who loved music more than anyone and always worked hard for his performance".

It added that his funeral will be "carried out in the quietest manner with his family members and co-workers" as per his family's wishes.

The singer had posted an emotional final photo on his Instagram account on Nov 20. The photo had showed lyrics from a song by K-pop indie group Dear Cloud, which read "persistent scars and sighs of exhaustion, will they have stopped?"

The post led fans to speculate on Monday if the lyrics had been an indication of his imminent death.

A throng of them gathered in front of the Seoul hospital where his body was lying to mourn his death, according to photos posted on social media.

Many also posted tributes on social media, saying they could not believe the news.

"My deepest condolences goes to Jonghyun's family, friends, SHINee and Shawols (fans of SHINee). Please stay strong," user @dearbngtn wrote on Twitter.

Another user, Saii Lopez‏ @saiilopeeez, wrote: "Jonghyun, you've been through a lot of pain and it must have been hard but I do hope that you knew that a lot of people love you. You can rest now without any pain."