The earthquake, part of more than 60 seismic events registered since early Tuesday, took place at 3:35 a.m. (0135 GMT), the Italian Geophysics and Volcanology Institute (INGV) said.
The temblor "was felt by the population but according to initial checks no damage has been reported so far," the Italian Civil Protection agency said in a statement, Reuters reported.
The Phlegraean Fields is an area of volcanic craters on the western outskirts of Naples that is under constant monitoring for the risk of earthquakes or volcanic eruptions.
The area is prone to bradyseism, the slow lifting or lowering of the ground. Lifting phases "are accompanied by intense local seismic activity", the civil protection said on its website.
MP/PR