Kumar, 90, was rushed to hospital and immediately wheeled into the ICU with complaints of breathlessness at 8.45pm on Sunday.
A source at the hospital said he had suffered a heart attack but at present the doctors were focusing on stabilising him. "There is no procedure slated as of now," added the source.
However, last evening the hospital authorities had denied any heart attack.
Dilip Kumar was born Muhammad Yusuf Khan on December 11, 1922, in Peshawar (now in Pakistan).
With a film career spanning six decades, he was the first to receive Filmfare Best Actor honour when the awards were started in 1954. With eight wins, Dilip Kumar shares with Shah Rukh Khan the record for the most number of Filmfare awards won in that category.
He was honoured with the Padma Bhushan in 1991 and the Dadasaheb Phalke Award in 1994 for his outstanding contribution to Indian cinema.
He was also nominated to Rajya Sabha for a term from 2000 to 2006.
In 1998, he was awarded the Nishan-e-Imtiaz, the highest civilian award conferred by the government of Pakistan.
(With inputs from PTI)