Homes were evacuated and many schools closed after a flurry of earthquakes hit the area around Naples in southern Italy, the BBC reports.
More than 160 earthquakes were recorded on Monday evening and overnight.
The strongest, of magnitude 4.4, happened around 20:00 local time (18:00 GMT) near the town of Pozzuoli. Italy’s National Institute of Geophysics and Volcanology (INGV) said it was the strongest quake in the region for 40 years.
Gaetano Manfredi, the mayor of Naples, acknowledged that residents may be scared – but said officials were “paying attention”.
Hundreds of tents were erected in Pozzuoli and some residents stayed on the streets for much of the night, though others opted to stay elsewhere with relatives.
While no significant damage to structures has been reported, some schools in Naples remained shut on Tuesday for inspections – and a women’s prison in Pozzuoli was evacuated as a precaution.
Mr Manfredi warned “there could be more serious quakes” in the future and said officials needed to “manage this emergency situation with which we might have to live for months”.
“I can’t tell people not to be scared, because that’s normal, but I can tell Neapolitans that we are paying attention and monitoring [the situation],” he continued in a statement.
“Never before has this territory been more closely watched, so let’s try and live as normally as we can.”
