Fans and fellow performers on Tuesday mourned the death of a K-pop star who had long been the target of online bullying, some calling for greater mental health support for those working in the country's notoriously competitive show business industry.

The body of Sulli, a former member of top girl group f(x), was discovered Monday by her manager at her home on the outskirts of Seoul.

"There has been no evidence of an outsider having broken in, or any other crimes committed by another person," an official from Seongnam Sujeong Police Agency told AFP.

"Suicide is among the possible causes."

Authorities said the 25-year-old had been suffering from "severe depression".

South Korea has one of the world's highest rates of suicide which, according to recent government figures, is among the top causes of death for those under 40.

"I wish I could hope for Sulli to be the last idol to die from suicide and mental illness," tweeted one fan.

"But knowing how cruel society is, I can't help but be afraid about who's going to be the next one."

Beneath the glitz and glamour, the K-pop industry is known for its cut-throat competitiveness, a lack of privacy, online bullying and relentless public pressure to maintain a wholesome image at all times and at any cost.

MENTAL HEALTH TABOO

K-pop stars like Sulli are picked up by agencies at a young age -- usually in their early- or mid-teens -- and their lives then taken over by gruelling singing and dancing training.

Taboos about mental illness dissuade many South Koreans from seeking help.

Sulli's death echoes that of fellow K-pop star Jonghyun, who took his life in 2017 after battling with depression.

Both were members of the SM Entertainment stable, one of the country's biggest talent agencies.

K-pop singer Goo Hara, a close friend of the late star, was also sent to hospital last year after a suspected suicide attempt. Goo had been abused by her ex who threatened to post her spycam sex vidoes online.

"I hope Jin-ri is now in a place where she can do whatever she wants," Goo wrote on Instagram -- using Sulli's real name and sharing photos of the two of them together.

Sulli, who started her career as a child actress at age 11, made her debut in 2009 for f(x), which quickly became one of K-pop's top girl groups.

Known for behaviour considered controversial in South Korea -- including her refusal to wear a bra in public -- she had been relentlessly bullied online throughout her career, with many sexually abusive comments.

She recently hosted a TV series where celebrities discussed their experiences of online abuse. She had also candidly shared her experience struggling with panic disorder and social phobia.

Her outspokenness resonated with many young South Korean women who have been leading a new wave of feminists fighting a patriarchal society obsessed with looks.

"Being one of the first female artists in K-pop to talk about mental health and feminism is amazing. I love you so much Sulli - I hope in heaven you are finally free," a fan wrote in a tweet.