Dr Ram Narain, Chief Operating Officer at Kokilaben hospital said, "He is extremely critical and on ventilator. He is on a high dose of medication to support his blood pressure. We hope to see some improvement through the day."
"But we will continue to keep a watch on him," he said.
The 83-year-old actor's son Vindu Dara Singh confirmed that his father was serious. "He is serious. There is blood clot in his brain or he has suffered heart attack... We are not sure what has happened. We have been told that he is under observation for 24 hours," Vindu said.
Dara Singh, who won the title of Rustam-e-Hind in wrestling, entered movie world in the 1960s. He appeared in various films such as Watan Se Door, Daada, Rustom-E-Baghdad, Sher Dil, Sikandar E Azam, Raaka, Mera Naam Joker and Dharam Karam. He was last seen in a 2007 release Jab We Met where he played Kareena Kapoor's grandfather.
The veteran actor also played the role of Hanuman in Ramanand Sagar's television series Ramayan.