Tamil Nadu Chief Minister J Jayalalithaa, who suffered a cardiac arrest on Sunday, died at 11.30 pm on Monday. She was 68.
As she remained critical for two days, the hospital had said she was "responding" to the treatment being given by experts, who included a four-member AIIMS team. Apollo Hospital said she had been on life support.
The Centre had earlier in the day dispatched a team of specialists from the All India Institute of Medical Sciences to the Apollo Hospital where Jayalalithaa was undergoing treatment after suffering cardiac arrest late yesterday.
Earlier, a London-based medical consultant who is assisting doctors treating the leader said Tamil Nadu Chief Minister J Jayalalithaa's condition is "extremely grave".
"The situation is extremely grave but I can confirm that everything possible is being done to give her the best chance of surviving (the cardiac arrest)," Richard Beale said in a statement.
Beale, from the London Bridge Hospital, had been regularly consulted by doctors at the Apollo Hospitals here ever since Jayalalithaa was admitted in September.
Crowds began to mass outside the hospital from Sunday evening as news that Jayalalithaa had suffered a cardiac arrest spread like wild fire.
A large number of police personnel were deployed at the Apollo hospital. Security was also stepped up across the sprawling state where Jayalalithaa enjoys widespread support.
Tamil Nadu ministers and legislators gathered at the hospital along with a mass of AIADMK activists and Jayalalithaa fans.
Some men and women, their hands folded, had offered silent prayers for Jayalalithaa’s early recovery. Some tried to enter the hospital premises but were restrained.
Jayalalithaa’s posters were held high by her supporters. Fans also offered special prayers in temples.
Some parts of Chennai experienced shortages of milk as traders jacked up prices fearing a shutdown.
Meanwhile, authorities in Kerala strengthened security on the border with Tamil Nadu. Police were put on alert in Thiruvananthapuram, Kollam, Idukki and Palakkad districts that border Tamil Nadu.