Three regions in northeast Italy which have been hit by strong quakes in the past two weeks sought to reassure tourists on Monday, telling them their beaches were safe as the summer season began.

"Continue to choose the welcoming and safe beaches of the northern Adriatic coast," said the presidents of the Emilia Romagna, Veneto and Friuli-Venezia Giulia in an appeal addressed to "foreign and Italian tourists."

The area cannot afford to lose the tourist industry after the tremors on May 20 and 29 caused costly damage to buildings, factories and warehouses.

Germans and Austrians in particular flock to summer resorts in Rimini and Riccione, but reports are emerging of anxious people cancelling their bookings.

"We ask our international guests to continue to visit us in order to avoid unjustly penalising us. The best way to help those who are suffering today is to chose our tourist destinations," the region's appeal said.

"The north Adriatic coasts are as safe and competitive as usual. All roads, motorways and airports are open," it said.

A 5.1-magnitude quake hit the region on Sunday as aftershocks continue to terrorise people living in temporary tents camps after May's quakes, which toppled buildings and left 23 people dead.

Italy marked the tragedy with a day of national mourning on Monday.