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

“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.

Jayalalithaa had not been seen in public since September. But the hospital had said her health was improving until she suffered a cardiac arrest on Sunday evening.

The Press Trust of India said police across the state had been put on high alert to maintain law and order, with 1,000 officers stationed at the hospital alone.

Media reports said some Chennai schools would remain closed, while the US consulate in the city said it had suspended services and warned Americans to exercise caution.

Several of her supporters resorted to self-harm when she was briefly jailed in 2014 on charges of corruption.

Jayalalithaa earned the loyalty of many voters in Tamil Nadu with a series of highly populist schemes, including an “Amma canteen” that provides lunch for just three rupees.

In 2014 she was briefly forced to step down as chief minister after she was jailed on corruption charges.

Her conviction, later overturned on appeal, sparked mass protests and even some reported suicides.

Thousands of directors, actors and producers in the successful Tamil language film industry went on hunger strike to demand her release.