An Italian murderer who was serving life in prison has escaped for the third time at least, a police union has said.

Giuseppe Mastini, 60, nicknamed "Johnny the Gypsy", took advantage of a temporary release from a high-security jail in Sardinia to flee, failing to return to his cell on Saturday, the ES Polizia union said.

Police are on the hunt for the prisoner.

Originally from Bergamo in northern Italy, Mastini moved to Rome in the 1970s with his family and committed his first murder aged 11, according to Italian news agency ANSA.

He first escaped from jail in 1987, when he failed to show up after a temporary release from prison.

He was on the run for two years, during which time he committed robberies, murdered a police officer, injured another, and took a young girl hostage.

Caught and jailed again, he was given another temporary release in 2014 which was filled with "irregularities," the union said, although it was unclear whether he fled that time round.

But in June 2017, he once again escaped from a prison in northern Italy, following the same method.