They say Mr Demirel, who held office in 1993-2000, died early in the morning in Guven Hospital in the capital, Ankara.
He had reportedly been treated for a respiratory tract infection.
In a political carrier spanning nearly 50 years, he also served seven times as the country's prime minister. His government was twice overthrown by the country's powerful military.
Mr Demirel - who led the Justice Party in 1964-90 - and a number of other politicians were banned from politics after a military coup in 1980.
The ban was lifted in 1987, paving the way for Mr Demirel's return to power several years later.
BBC
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