Two young men are "lucky to be alive" after the car they were traveling in was swallowed by a huge sinkhole that opened up early on Wednesday in a road in Naples's Vomero district.

The pair, who were returning from a party after a university exam, were saved by Army soldiers who happened to be stationed in the area as part of the Strade Sicure (Safe Streets) operation.

A parked car also fell into the sinkhole.

"It's a miracle we are alive.

It could have gone much, much worse," said Giulio Delle Donne, one of the two young men who is also a municipal councillor.

"We are alive thanks to the fast response of the Army military personnel.

"Less than a second after (the car plunged into the sinkhole) a tree fell and a water pipe broke.

"Three soldiers from the Campania Group of the Italian Army engaged in the Strade Sicure operation who were in the area came and saved us.

A passer-by came too.

"It was just after 4am.

"The water pipe broke and we could have been submerged in water.

"Luckily, we got out of it with just a few scratches.

"After all these (similar) events, let's hope they finally decide to map out the state of the structures and systems".

Naples Mayor Gaetano Manfredi said that the problem is that the southern city has "a sewer system that has not had maintenance for many years.

"We are implementing a project for the continuous monitoring of the sewer-and-water network and this will allow us to carry out preventive maintenance," he added.