DMK chief M Karunanidhi, being treated for fever due to urinary tract infection, was shifted to a private hospital from his residence in Chennai early today due to dip in blood pressure and is now stable, the hospital said.
The 94-year-old leader was admitted to the Intensive Care Unit of Kauvery Hospital around 1:30 am.
A medical bulletin issued at 8 pm said "former Chief Minisiter Karunanidhi's health condition continues to remain stable with ongoing active medical support. He is continuously being monitored and treated by the panel of expert doctors in the ICU."
Earlier the hospital said he was admitted after his blood pressure had dropped.
"His blood pressure has been stabilised with medical management and he continues to be monitored and treated by a panel of experts," the 2.30 am bulletin said.
Mr Karunanidhi's family members discussed the treatment modalities with hospital authorities.
DMK leaders, including party working president and Mr Karunanidhi's son MK Stalin, and other frontline leaders such as Duraimurugan, Rajya Sabha MP Kanimozhi and former Union minister A Raja were present at the hospital.
The DMK leaders had also visited Mr Karunanidhi's house in Gopalapuram area before he was taken to the hospital.
Mr Karunanidhi's estranged son and former DMK leader MK Alagiri, who was expelled from the party by the DMK chief in January 2014 after a prolonged struggle for power with his younger brother MK Stalin, also visited his father's house and the hospital.
Governor Banwarilal Purohit and Defence minister Nirmala Sitharaman visited the hospital and enquired about the health of Mr Karunanidhi with hospital authorities, MK Stalin and other members of the DMK president's family.
Chief Minister K Palaniswami told reporters at Salem that the state government was ready to provide all possible medical assistance to the ailing Mr Karunanidhi, who was a five-time chief minister, if it was approached.
Kerala Chief Minister Pinarayi Vijayan, wishing a quick recovery, tweeted: "Kalaignar M Karunanidhi is a born fighter. I am sure he will fight back and return fast to good health. Wish him a speedy recovery."
Delhi Chief Minister Arvind Kejriwal tweeted, "My prayers for Sh Karunanidhi's fast recovery."
State health minister C Vijayabaskar too wished the DMK chief a speedy recovery.
After receiving the news about Mr Karunanidhi being admitted to hospital, party cadre from various parts of the state poured in there chanting "long live Thalaivar" (leader) and "meendu vaa thalaiva," (come back leader).
Hours before Mr Karunanidhi was moved to the hospital, MK Stalin had said the former chief minister's health was improving.
On Wednesday, he had assured people that there was nothing to worry about his father's health.
Security was tightened at the former chief minister's residence as DMK cadres thronged the area.
Later in the day, senior Congress leaders Ghulam Nabi Azad and Mukul Wasnik visited members of Mr Karunanidhi's family and spoke to doctors at the hospital.
"Karunanidhiji is totally stable... he is improving... we are praying for his speedy recovery," Mr Azad told reporters, adding the Congress high command had directed them to enquire about his health.
State Congress leaders, including EVKS Elangovan, TNCC chief Su Thirunavukkarasar, were present at the hospital.
Actors including Prabhu and Nasser also paid a visit to the hospital.
Meawnhile, Hashtag #KarunanidhiHealth is trending on Twitter.
For the past two years, though Mr Karunanidhi did not make any public appearance owing to ill-health, he had visited the party headquarters and still holds the top post in the Dravidian party.
On July 18, the leader had underwent a procedure to change his tracheostomy tube to help him in breathing.
Mr Karunanidhi, who is addressed as 'Kalaignar' (artiste) by his supporters, followers and some politicians, entered his 50th year as party chief on Friday.