According to the Portuguese IPMA Sea and Atmopshere Institute, mainland seismic stations recorded the quake just outside Arraiolos, which forms part of the Alentejo district of Évora.

Fire-fighters in Arraiolos said "everything was shaking", and that they were inundated with calls, but said they had no reports of any damage.

The earthquake was felt across the country, especially by people living in tower blocks.

One distressed reader told The Portugal News he "was seated on his 12th floor balcony in Quarteira when everything started shaking."

There were also reports of children being evacuated from schools in nearby Elvas.

IPMA recalled that locating the epicentre of an earthquake "is a complex physical and mathematical process that depends on the set of data, algorhythms and propagation models of seismic waves," noting that "different agencies may produce slightly different results."

"Similarly, the preliminary determinations are usually corrected later, through the inclusion of more information," it added.