The scientist was brought to the KRL Hospital in Islamabad after his health started deteriorating on Saturday night, Geo TV said.
According to sources, Khan was hospitalised after he experienced discomfort in breathing. However, his health took a turn for the worse when his lungs started bleeding, the news outlet added.
Abdul Qadeer Khan became a national hero after Pakistan conducted nuclear tests in May 1998, becoming the sole nuclear power in the Muslim world and the seventh country to possess nuclear weapons.