The quake, which was followed by several much smaller tremors, was the biggest to hit the Campi Flegrei (Phlegraean Fields) area in southern Italy for 10 months.

It occurred around 1:25 am (0025 GMT) at a depth of 2.5 kilometres, according to the National Institute of Geophysics and Volcanology (INGV), and raised residents from their beds.

"We can't go on like this, we can't sleep. We're scared," one man told the Local Team news service in the middle of night in Bagnoli, a seaside district in western Naples.

Images broadcast by Italian media showed car windows smashed by falling masonry and damage to a church in Bagnoli, where schools were closed on Thursday.

One women was hurt when her ceiling collapsed, while two or three other people went to hospital with cuts caused by shards of broken glass, according to Naples mayor Gaetano Manfredi.

A total of 11 people went to emergency rooms of local hospitals but several "were cases of panic", he told reporters.

Prime Minister Giorgia Meloni said she was constantly monitoring the situation and was in contact with the relevant officials.

Seismic activity is nothing new in the area, which is an active caldera -- the hollow left after an eruption -- the largest in Europe.

It stretches from the outskirts of Naples into the sea, measuring some 12 by 15 kilometres (7.4 by 9.3 miles).

But many of the 500,000 inhabitants living in the danger zone had already been spooked by a 4.4-magnitude quake in May 2024, which was the biggest for 40 years.

At that time, there were no injuries or any major structural damage.

- 'Particularly intense' -

Naples mayor Manfredi told RTL radio that Thursday's quake was a "particularly intense tremor", similar to that of last year but "with an epicentre closer to the city of Naples, so it was felt more in the city".

He said a group of people tried to enter the closed former NATO base in Bagnoli, presumably for protection.

"There was a moment of panic... but then everything calmed down," he said, adding: "Obviously these are moments in which people are afraid."

Manfredi said the situation was "under control".

The eruption of Campi Flegrei 40,000 years ago was the most powerful in the Mediterranean.

A resurgence of seismic activity in the early 1980s led to a mass evacuation which reduced the nearby city of Pozzuoli to a ghost town.

Specialists, however, say a full-blown eruption in the near future remains unlikely.