Hundreds of thousands of protesters have rallied in Rome to protest Prime Minister Matteo Renzi's plans for job reform.

Two marches took place in the heart of the Italian capital, snarling traffic for hours.

Protesters cheered CGIL union head Susanna Camusso when she promised more protests and strikes unless Mr Renzi abandons efforts to make it easier for employers to fire workers.

The centre-left premier contends employers now fear hiring workers they cannot dismiss in case business sours. He said the measure would help heal Italy's recession-mired economy.

Nationwide, unemployment tops more than 12 per cent. Nearly one of every two youths is unemployed, with many going abroad to find work.