US author William H. Gass, who worked on his mega-novel "The Tunnel" for three decades, has died at the age of 93, his French publisher said Thursday.

The author, known for a bleak style which earned him comparisons to William Faulkner, died Wednesday, publisher Cherche-Midi said, without saying where.

Clocking in at some 650 pages, “The Tunnel” — published in 1995 after some 30 years of work — won the American Book Award for its dark depiction of a historian specialising in Nazi Germany.

The New York Times described the book, famed for its complexity and dense style, as “maddening, enthralling, appalling, coarse, romantic, sprawling, bawling”.

Born in Fargo, North Dakota, Gass also won plaudits for his debut novel “Omensetter’s Luck” (1966) detailing life in rural Ohio as well as his third book, “Middle C”.

He also published three collections of short stories, a book of novellas, and many essays.

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