"There was a transient setback in the clinical condition of Kalaignar Dr. M Karunanidhi, DMK President and former Chief Minister of Tamil Nadu. With active medical support, his vital signs are normalising," the hospital said in a statement.
He continues to be closely monitored by the panel of expert doctors, the medical bulletin said.
Following a dip in his blood pressure, Karunanidhi was admitted to the hospital on Saturday. On July 18, he had undergone a procedure at the same hospital to change his tracheostomy tube.
Earlier on Sunday, Vice President M Venkaiah Naidu visited a private hospital here to inquire about the health condition of M Karunanidhi.
The DMK, meanwhile, released a photograph, the first after Karunanidhi's hospitalisation early on Saturday, showing Naidu standing beside the 94-year-old leader in his hospital bed.
Party cadres outside the hospital were enthused by the release of the image.
They said the picture did not feature any "life support system like a ventilator" and it was reassuring that their Thalaivar (leader) was recuperating well.
DMK had, during the hospitalisation of late Chief Minister J Jayalalithaa in 2016, asked why no photograph of her in the hospital was released.
The party had said that release of a picture would have helped put at rest speculations about her health status.
Tamil Nadu Governor Banwarilal Purohit, DMK working president M K Stalin, party Rajya Sabha MP Kanimozhi, the nonagenarian leader's wife Rajathi Ammal and Karunanidhi's personal physician Dr Gopal are also seen in the picture.
Naidu said doctors informed him that Karunanidhi's condition was stable.
(With inputs from PTI)