Well-known Bollywood singer Krishnakumar Kunnath, popularly known as KK, died in Kolkata on Tuesday night, officials said.
He was 53, and survived by wife and two children.
KK performed at a concert organised by Gurudas College at Nazrul Mancha in south Kolkata for almost an hour in the evening.
He was "feeling heavy" after reaching his hotel, and soon collapsed, officials said.
He was taken to a nearby private hospital where doctors declared him brought dead, they said.
"KK was brought to the hospital around 10 pm. It's unfortunate that we could not treat him," a senior official of the hospital said.
Doctors at the hospital said they suspected "cardiac arrest" to be the cause of the death.
A senior officer of the Kolkata Police told PTI that a post-mortem would be conducted on Wednesday to ascertain the exact reason for the death.
Condoling his death, Prime Minister Narendra Modi said KK will always be remembered through his songs.
"Saddened by the untimely demise of noted singer Krishnakumar Kunnath popularly known as KK. 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," Modi tweeted.
His wife and children will reach Kolkata on Wednesday morning.
KK, who was on a two-day tour to Kolkata, also performed at Nazrul Manch on Monday evening in a concert organised by Vivekananda College. He was supposed to return to New Delhi on Wednesday.
"I have so many personal memories with him. We started our careers together. He was such a nice and non-controversial person. Life has become so unpredictable and uncertain after the pandemic," singer-turned-politician Babul Supriyo told reporters after reaching the hospital.
"KK has a big contribution to the advent of rock music in India," said Supriyo, a TMC MLA.
A police team was posted outside the hospital to manage KK's fans who started gathering after hearing the news of his death.
Shibasis Banerjee, a student of Gurudas College who attended Tuesday's concert, said the singer was full of energy during the show.
"He posed with us for selfies and also gave us autographs when we requested," he said.
"He performed one song after another on the stage. A huge number of people gathered to see him. It is unbelievable that he is no more. I met him at such a show during the initial days of my college, when I told him that today, he instantly recognised me," Shibasis said.
Initial hits such as 'Pyaar Ke Pal' and 'Yaaron' made KK popular among the youths of the country.
As a playback singer, he has recorded Bollywood numbers such as 'Ankhon Mein Teri' (Om Shanti Om), 'Zara Sa' (Jannat), 'Khuda Jaane' (Bachna Ae Hasino) and 'Tadap Tadap' (Hum Dil De Chuke Sanam).
A versatile singer, KK has also recorded songs in Tamil, Telugu, Kannada, Malayalam, Marathi, and Bengali, among other languages.
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