Some 900 earthquakes hit southern Iceland on Monday, authorities said, adding to tens of thousands of tremors that rattled the region in recent weeks as the country braces for what could become a significant volcanic eruption.
It comes as Iceland officials worked to build a wall around a nuclear facility to stop any lava flow nearby.
Experts have said residents will get just 30 minutes warning ahead of any explosion.
Almost 4,000 people were evacuated over the weekend as authorities feared that molten rock would rise to the surface of the earth and potentially hit a coastal town and a geothermal power station.
"We have this tremendous uncertainty now; will there be an eruption and if so, what sort of damage will occur," said Matthew James Roberts, director of the service and research division at the Icelandic Meteorological Office.
Inhabitants of the town of Grindavik described being whisked from their homes in the early hours of Saturday as the ground shook, roads cracked and buildings suffered structural damage.
Hans Vera, a Belgian-born 56-year-old who has lived in Iceland since 1999, said there had been a constant shaking of his family's house.
"You would never be steady, it was always shaking, so there was no way to get sleep," said Vera, who is now staying at his sister-in-law's home in a Reykjavik suburb.
"It's not only the people in Grindavik who are shocked about this situation it's the whole of Iceland," he said.
Almost all of the town's 3,800 inhabitants had been able to find accommodation with family members or friends, and only a between 50 and 70 people were staying at evacuation centres, a rescue official said.
Some evacuees were briefly allowed back into the town on Sunday to collect belongings such as documents, medicines or pets, but were not allowed to drive themselves.
"You have to park your car five kilometres from town and there's 20 cars, huge cars from the rescue team, 20 policemen, all blinking lights, it's just unreal, it's like a war zone or something, it's really strange," Vera said.
The Reykjanes peninsula is a volcanic and seismic hot spot southwest of the capital. In March 2021, lava fountains erupted spectacularly from a fissure in the ground measuring between 500 750 metres long in the region's Fagradalsfjall volcanic system.
Volcanic activity in the area continued for six months that year, prompting thousands of Icelanders and tourists to visit the scene. In August 2022, a three-week eruption happened in the same area, followed by another in July of this year.
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