A famous pizzeria in Naples that was bombed in a possible act of intimidation by the Camorra mafia has received messages of solidarity from around the world.

Supporters placed a message on the damaged entrance to the eatery on Thursday which read: “If you mess with pizza, you mess with Naples.”

The outpouring of support coincided with World Pizza Day, an Italian initiative that celebrates the skills and knowledge of the traditional “pizzaiolo” or pizza maker.

Police are investigating the explosion outside the Sorbillo pizzeria, in the heart of Naples, which happened when the restaurant was closed and did not injure anybody.

In the aftermath of the attack, the owner, Gino Sorbillo, posted a photograph on social media of himself holding a handwritten sign which read: “Closed because of a bombing. But we’ll reopen soon.”

He said the bombing was “an attack on legality and on the renaissance of Naples,” which is striving to jettison its reputation for petty crime and poverty.