LISBON—Authorities on a mid-Atlantic Portuguese island hit by thousands of small earthquakes in recent days started evacuating people living at the bottom of coastal cliffs on Thursday as fears of a stronger tremor or a volcanic eruption grow. Since Saturday, over 2,000 earthquakes, with a magnitude of between 1.6 and 3.3, have been recorded on the volcanic island of Sao Jorge in the Azores archipelago, according to the region’s CIVISA seismo-volcanic surveillance centre. The small quakes, which have caused no damage so far, were reported along the island’s volcanic fissure of Manadas, which last erupted in 1808. A big earthquake hit the island in 1980, causing severe damage. CIVISA has raised the volcanic alert to level 4 out of 5, meaning there is a “real possibility of eruption,” and said the number of earthquakes was above normal levels. Those in hospital or in care homes in the municipality of Velas, …