Sushma Swaraj, former foreign minister and one of the ruling Bharatiya Janata Party’s (BJP) tallest leaders died on Tuesday night at Delhi's All India Institute of Medical Sciences, local media reports said.
A number of her party colleagues and ministers have already reached the premier hospital. Among the first to arrive were Nitin Gadkari, Dr Harshvardhan, Rajnath Singh and Smriti Irani.
On Twitter, PM Modi described her as a "prolific orator and outstanding parliamentarian" who was "admired and revered across party lines".
Ms Swaraj was rushed to the hospital by her family sometime after 9 pm on Tuesday when she was taken ill.
The 67-year-old, who had a kidney transplant two years ago, had not been keeping well lately.
She had not contested the recently held Lok Sabha election and opted out of Prime Minister Narendra Modi's new government for health reasons. In June, she had moved out of her official residence.
Hours before her death, Ms Swaraj had tweeted congratulating Prime Minister Narendra Modi over the passage of the Jammu and Kashmir Reorganisation bill in parliament.
“Thank you Prime Minister. Thank you very much. I was waiting to see this day in my lifetime”, she tweeted addressing Modi.
"India grieves the demise of a remarkable leader," said PM Modi on Twitter, describing her as "an excellent administrator" and praising her for "her compassionate side, helping fellow Indians who were in distress in any part of the world."
Prime Minister Modi, in his tweets, hailed Swaraj as a "prolific orator and outstanding parliamentarian" and said she was admired and revered across party lines.
"She was uncompromising when it came to matters of ideology and interests of the BJP, whose growth she immensely contributed to," Modi said.
He added: "An excellent administrator, Sushma Ji set high standards in every Ministry she handled. She played a key role in bettering India's ties with various nations. As a minister we also saw her compassionate side, helping fellow Indians who were in distress in any part of the world."
"Extremely shocked to hear of the passing of Smt Sushma Swaraj. The country has lost a much loved leader who epitomised dignity, courage & integrity in public life. Ever willing to help others, she will always be remembered for her service to the people of India," President Ram Nath Kovind tweeted.
Defence Minister Rajnath Singh said he was deeply shocked and anguished by the sudden demise of an extremely valued colleague. External Affairs Minister S Jaishankar said, "Deeply shocked to learn of the passing away of Smt Sushma Swaraj. Difficult to accept this news. The whole nation grieves, the Foreign Ministry even more so."
The Congress condoled her demise. "We are saddened to hear about the untimely demise of Smt Sushma Swaraj. Our condolences to her family and loved ones," the party said.
"I'm shocked to hear about the demise of Sushma Swaraj Ji, an extraordinary political leader, a gifted orator & an exceptional Parliamentarian, with friendships across party lines. My condolences to her family in this hour of grief. May her soul rest in peace. Om Shanti," Congress leader Rahul Gandhi said on Twitter.
Swaraj had a kidney transplant in 2016 and had opted out of contesting Lok Sabha polls earlier this year for health reasons. She is survived by her husband Swaraj Kaushal and daughter Bansuri.