Gandhi, accompanied by TNCC president Su Thirunavukkarasar, among others, briefly interacted with Karunanidhi's son and DMK working president M K Stalin and laid a wreath before the mortal remains of Karunanidhi.
Expressing grief over the death, Gandhi had said that the DMK patriarch strode the stage of Tamil politics like a colossus for six decades.
Azad said as chief minister, Leader of Opposition and a party chief, Karunanidhi was known and respected across the country.
"Today he is no more but his work and ideology will always remain a guiding factor for all of us. The void (created by Karunanidhi's demise) cannot be filled by any political leader.
It is a great loss to the country, to the party and to all those who are directly or indirectly associated with him," he said.
Moily hailed Karunanidhi as a "champion of social justice."
Karunanidhi, 94, died at a private hospital yesterday following prolonged illness.