"There has been a significant decline in the clinical condition of Dr M Karunanidhi over the last few hours. Despite maximum medical support, his vital organ functions continue to deteriorate," the hospital said.
His condition is extremely critical and unstable, it said.
A large number of DMK cadres and supporters continued to mass in large numbers outside the Kauvery Hospital where Karunanidhi, 94, has been admitted since July 28. The security outside the hospital has also been stepped up.
Earlier in the day, Karunanidhi's son and party working president M.K. Stalin met Tamil Nadu Chief Minister K. Palaniswami in Chennai. The meeting took place at Palaniswami's residence, IANS reported and added that Stalin was accompanied by some party colleagues.
"Ezhundhu Vaa Thalaivaa" (Awake, our leader) and "Vaa, Vaa, Gopalapuram Polaam Vaa" (Come, Come, let's go to Gopalapuram) were among the slogans raised by the emotionally-charged crowd, referring to the locality where the former Tamil Nadu Chief Minister has a house.
Hundreds of men and women have assembled outside the hospital located in Alwarpet in south Chennai. "We want to hear the good news about our leader's health. That is why we are here," said a party member.
The crowd outside the hospital started to swell after the medical bulletin issued by Kauvery Hospital on Monday evening said that Karunanidhi's condition had deteriorated.
"There has been a decline in the medical condition of DMK president and former Chief Minister M Karunanidhi. Maintaining his vital organ functions continues to remain a challenge considering his age-related ailments," the Kauvery hospital had said on Monday.
"His response to the medical interventions over the next 24 hours will determine the prognosis," the medical bulletin said.
The DMK leader's condition turned bad on July 28 with a drop in his blood pressure and he was shifted to the hospital. He has remained there since then.
(With inputs from IANS)