Jayalalithaa Jayaram, the chief minister of south India's Tamil Nadu state and one of the country's most popular political leaders, has died after a prolonged illness, hospital authorities announced late Monday night, AFP reported

"It is with indescribable grief, we announce the sad demise of our esteemed honourable chief minister of Tamil Nadu ... at 11:30pm (local time) today (December 5)," Chennai's Apollo Hospital said in a statement released to the media.

Doctors had been treating the 68-year-old former film star, who enjoys an almost god-like status in Tamil Nadu.

Hundreds of devotees have kept a round-the-clock vigil outside the private hospital in the state capital Chennai since she was first admitted in September suffering from a fever. Their numbers have swelled since her condition worsened on Sunday.

Prime Minister Narendra Modi offered his condolences.

"I will always cherish the innumerable occasions when I had the opportunity to interact with Jayalalithaa ji (honorific). May her soul rest in peace," Modi said on Twitter.

Her political party, AIADMK, on Twitter said: "our beloved leader, the Iron lady of India... Amma, is no more."

To millions of her followers, the chief minister was known simply as "Amma" (mother).

The party also announced that her body would be kept at a prominent public hall in the city for people to pay their last respects.