One of India’s most popular and powerful politicians, J Jayalalitha, remains in a critical condition after suffering a heart attack on Sunday night, the hospital treating her said.
Thousands of people are standing vigil outside the hospital.
Ms Jayalalitha has been receiving treatment for months and was last seen in public in September.
The former film star has been Tamil Nadu chief minister four times and is revered by many in the state.
With the extreme devotion she inspires among her supporters, many of whom refer to her as “Amma” (mother), there are concerns that a serious deterioration in her condition could spark unrest.
Police have been put on alert across Tamil Nadu and outside her official residence.
News of her health over the last few months has been closely monitored and guarded, and in a sign of the sensitivity around the issue two people were arrested for spreading rumours about her health in October.