Iceland has declared a state of emergency after a series of earthquakes raised fears of a volcanic eruption.
Authorities have ordered thousands living in the southwestern town of Grindavík to evacuate as a precaution.
The Icelandic Met Office (IMO) says it is concerned that large amounts of magma – molten rock – is spreading underground and could come to the surface there.
Thousands of tremors have been recorded around the nearby Fagradalsfjall volcano in recent weeks.
They have been concentrated on Iceland’s Reykjanes Peninsula, which had remained dormant to volcanic activity for 800 years before an eruption in 2021.
Iceland’s civil protection agency said the decision to evacuate came after the IMO could not rule out that a “magma tunnel currently forming could reach Grindavík”.
In a statement on Friday, the agency said people should leave the city, but also stressed that it was not an “emergency evacuation” – urging them to “remain calm because we have plenty of time to react”.
“There is no immediate danger imminent, the evacuation is primarily preventive with the safety of all residents of Grindavík as the main objective,” it added.
All roads into the town of about 4,000 people are closed except for emergencies to ensure traffic can get in and out.
In a statement on Friday, the IMO said that “significant changes have occurred in the seismic activity”, with tremors moving towards Grindavík during the day.
It added that magma is likely to have extended beneath the city and it was “not possible to determine precisely” if or where it might emerge.
“The amount of magma involved is significantly more than what was observed in the largest magma intrusions associated with the eruptions at Fagradalsfjall,” the IMO said.
Iceland is one of the most geographically active regions in the world, with around 30 active volcanic sites.
Volcanic eruptions occur when magma, which is lighter than the solid rock surrounding it, rises to the Earth’s surface from deep beneath it.
In July, Litli-Hrutur, or Little Aries, erupted in the Fagradalsfjall area, drawing tourists to the site of the “world’s newest baby volcano”.
The site was dormant for eight centuries until eruptions in 2021, 2022 and 2023.