An Italian bomb squad officer has lost an eye and hand after a suspicious package he was examining exploded.

A package left outside a closed bookshop with links to a group of extreme right activists, CasaPound, caught the attention of a passing police patrol, Florence Police Chief Alberto Intini said.

The explosives squad was called to intervene at about 5am on Sunday and the officer was gravely injured, police spokesman Cesare Tarashi said.

Italy occasionally sees explosions that authorities have blamed on political extremists. The country suffered bombings, killings and kidnappings during a period of domestic terrorism in the 1970s and early 1980s.

Mayor Dario Nardella said peaceful Florence "isn't represented by the horrors" of the blast, which is being investigated.

Florence Cardinal Giuseppe Betori decried criminals who wanted a "bloody passage from the old year to the new".