According to the Korea Herald, Park died Thursday at a hospital, but she had first collapsed while at a friend's house ... and might have suffered a cardiac arrest -- but the exact cause of death is still under investigation.

Another report, from AllKPop, says one of Park's friends found her unconscious and slouched over a bathroom sink -- and one of her friends then performed CPR, attempting to revive her.

Park's agency, Xanadu Entertainment, confirmed the tragic news in a statement to AllKPop.

They shared ... "Our hearts are deeply troubled as we deliver this sudden news to her fans. A wake and funeral proceedings will be scheduled after a discussion with the singer's family."

Park first rose to stardom with her 2010 appearance on Mnet's "SuperStar K2" competition series.

She went on to release her first solo single in 2014, with a song called "Beautiful."

Park then nabbed an Artist of the Year award at the 4th Gaon Chart K-POP Awards. She would go on to be nominated for a Mnet Asian Music Award, Melon Music Award, and Golden Disk Award.

After her success with "Beautiful," Park released other chart-toppers, including "Celepretty," "Sorry," "Pretty Bae," "Ordinary Love," "Dynamic Love," "Will Be Fine" and "If You."

Park -- who released a new duet with "SuperStar K2" winner Huh Gak in February -- was reportedly set to release her studio album later this year.

She was only 30.