Hassan's son Asif Mehdi says his father died Wednesday. He was ill and unable to sing for 10 years.
Hassan was born in 1927 in what is now India but migrated to Pakistan with his family after the 1947 creation of the Muslim state.
In his early days, he worked at a bicycle shop and as a car mechanic before he gained fame for his mastery of the Ghazal, a traditional love poem expression put to music. He became known as the "King of Ghazal."
His songs rang out frequently across markets and buses, in homes across Pakistan and beyond, and were the soundtrack to more than 300 Pakistani films.