Former prime minister Manmohan Singh was admitted to the All India Institute of Medical Sciences (AIIMS) in Delhi after his health deteriorated on Thursday night.
The 92-year-old veteran Congress leader was brought to the emergency department of the hospital, PTI reported quoting sources. His condition is said to be critical.
The reason for his hospitalisation was not immediately known.
Congress leader Priyanka Gandhi Vadra has reached the hospital while party president Mallikarjun Kharge and former chief Sonia Gandhi are expected to arrive shortly.
BJP president J.P. Nadda has also arrived at the hospital.
Singh, who served as the prime minister in two consecutive terms from 2004 to 2014, retired as a Rajya Sabha MP in April this year. He had been a member of the upper house since 1991.
Singh is considered the key architect of India’s economic reforms which were implemented during his tenure as the finance minister in the P.V. Narasinha Rao-led government from 1991-1996.
He also served as the Leader of the Opposition in Rajya Sabha from 1998 to 2004.