Around 1,100 small earthquakes have rattled one of Portugal’s mid-Atlantic volcanic islands in less than 48 hours, prompting authorities to activate an emergency plan as experts assess what they have described as a seismic crisis. Multiple, small earthquakes that have been rattling a mid-Atlantic Portuguese island for three days could trigger a stronger tremor or a volcanic eruption, as authorities urged people not to travel there.

Sao Jorge, one of nine islands that make up the Azores, is home to around 8,400 people and is part of the archipelago’s central group, which includes the popular tourist destinations of Faial and Pico, which are also volcanic.

The series of small quakes, known as a swarm and which have caused no damage so far, were reported along the island’s volcanic fissure of Manadas, which last erupted in 1808. Sao Jorge’s municipalities have activated emergency plans as a precaution.

It urged people to stay calm, stay informed and follow the recommendations of officials.