Seismologists issued aftershock warnings on Monday in southwestern Greece after yesterday a 6.5 aftershock killed two people and injured about 150 other.

Numerous aftershocks followed the main tremor including one measuring 4.7 degrees on the Richter scale, said Giorgos Stavrakakis, head of the Athens Geodynamic Institute. The seismology specialist added that the next few days are critical for Greece’s residents.

The earthquake struck Greece, which is one of Europe's most earthquake-prone countries, at 3:25 p.m. local time, the U.S. Geological Survey and Greek scientists said.

A 60-year-old man died as the roof of the house fell on him and an 80-year-old woman suffered a deadly heart attack during or after the quake, authorities said. Three members of a family and a child were reportedly trapped under rubble in a village in the south Pelopponese region, authorities said.

The tremor struck Sunday afternoon near the city of Patras, about 120 miles (200 kilometers) west of Athens. About 70 houses were wrecked in the provinces of Ahaia and Ilia. At least 30 other were damaged and 230 more were left with cracks, the Interior Ministry said Monday.

Evacuations were carried out by authorities in four apartment buildings damaged in the quake in anticipation of aftershocks that might level the buildings.

Greece lies in one of the globe’s most active earthquake areas, between Europe and Africa. A 5.9 earthquake hit Athens in 1999 killing 143 people.