Celebrated Indian musician KK, real name Krishnakumar Kunnath, has died aged 53.
Hours after the playback singer had been performing a concert in Kolkata, he collapsed in the hotel where he was staying.
The singer was dead by the time he arrived at the Calcutta Medical Research Institute, local media reported.
He reportedly felt sick while performing, complaining of feeling unwell after returning to his hotel from the concert at Nazrul Mancha auditorium.
The cause of death was not yet known, but Kolkata Police have registered an unnatural death case, India Today reported. The publication quoted police sources as saying that there were injuries on KK's face and head.
The body has been sent for post-mortem, West Bengal Sports and Youth Affairs Minister Aroop Biswas told journalists. He said family members had been informed and were "likely to reach Kolkata on Wednesday morning".
A video of his final performance has since gone viral, showing the star "sweating profusely", although he later is reported to have complained of feeling extremely cold.
KK was known for songs such as Pyaar Ke Pal and Yaaron, which were big hits when he was a teen in the late 1990s. His 1999 debut album Pal was much loved and he forged a successful career in playback singing, recording songs for Bollywood films.
He recorded in several languages, including Hindi, Tamil, Telugu, Malayalam and Bengali.
Fans, celebrities and politicians shared their condolences on social media.
Indian Prime Minister Narendra Modi led the tributes.
"Saddened by the untimely demise of noted singer Krishnakumar Kunnath popularly known as KK," Mr Modi wrote on Twitter.
"His songs reflected a wide range of emotions as struck a chord with people of all age groups. We will always remember him through his songs. Condolences to his family and fans. Om Shanti."
Politician Rahul Gandhi wrote: "Krishnakumar Kunnath, fondly known as KK, was one of the most versatile singers of the Indian music industry. His soulful voice gave us many memorable songs.
"Saddened by the news of his untimely demise last night. My heartfelt condolences to his family & fans across the world."
Fellow playback singer Mohit Chauhan also mourned the death of the musician.
"This was the last time we were together to announce a tour together," he wrote online.
"How can you just go??? In shock. In grief. A dear, dear friend, a brother is gone. RIP KK. Love you."
KK is survived by his wife, Jyothy, and their two children, Nakul Krishna Kunnath and Tamara Kunnath.
