And it asked the people to pray for "Amma's", which is what Jayalalithaa is fondly called by her supporters, speedy recovery. Amma means "mother".
Media reports added that a large number of cadres from Jayalalithaa's party -- the All India Anna Dravida Munnetra Kazhagam or AIADMK -- have gathered outside Apollo Hospital.
The Press Trust of India reported that the supporters had begun to gather Sunday evening itself after the news broke to pray for Jayalalithaa's recovery, and that the late-night rains that fell in Chennai did not deter them.
The Press Trust of India added that ministers from the AIADMK also remained overnight at the hospital, but that they did not speak to the media.
The Press Trust of India reported that the hospital itself has been put under a thick blanket of security, with police also barricading off approach routes to the hospital ostensibly to "prevent traffic jams".
State police chief, director general of police TK Rajendran, meanwhile has asked all police personnel to report for duty.
"They should report in full uniform with their vehicles for law and order bandobust duty until further orders," PTI reported him as saying.
Jayalalithaa has been admitted at Apollo Hospital since September 22, when she complained of fever and dehydration. She was later treated for infection and a respiratory problem.
Before Sunday evening's announcement that she had suffered a cardiac arrest, reports coming out of Apollo had said the chief minister was on the mend and also that she would soon be discharged.