An earthquake measuring 3.5 on the Richter scale was felt across parts of the Alentejo in the early hours of Monday morning, according to the Portuguese Institute for Sea and Atmosphere (IPMA).
The earthquake was recorded at 3.08am, with its epicentre around 18 kilometres east of Odemira.
It was felt most strongly in the municipality of Ourique, in the Beja district, where it reached a maximum intensity of IV on the Modified Mercalli scale.
The tremor was also felt with lower intensity in Almodôvar (Beja district) and Santiago do Cacém (Setúbal district).
No injuries or material damage were reported.
An intensity IV earthquake is generally strong enough to be noticed by many people indoors. According to the IPMA’s description of the Modified Mercalli scale, hanging objects may swing and vibrations can resemble those caused by the passage of heavy vehicles.
Windows, doors, crockery and glassware may rattle, while stationary vehicles can also be seen rocking slightly.
The IPMA recorded another smaller earthquake shortly after midnight on Monday.
That tremor, measuring magnitude 2.5, occurred at 12.13am and had its epicentre around six kilometres east-southeast of Cape St Vincent, off the Algarve.
The IPMA said it had received no reports indicating that the second earthquake had been felt.
Small earthquakes of this magnitude are relatively common in Portugal and usually cause no damage.