The singer was hospitalised following a lung ailment, reported the Daily Times.
Hassan's family has requested the nation to pray for his health, added the paper.
Affectionately called Khan Sahib, Mehdi Hasan has been bestowed with the title "Shahenshah-e-Ghazal". He is a legendry Pakistani Ghazal singer and a former playback singer for Lollywood.
He was born in the village of Luna in Rajasthan, India in 1927 into a family of rich traditional musicians, and claims to be the 16th generation of hereditary musicians.