The fishing town had been evacuated overnight on Saturday and no people were in danger, according to the authorities.
“No lives are in danger, although infrastructure may be under threat,” Iceland’s President Gudni Johannesson said on social media site X, further adding that there had been no interruptions to flights.
Live footage showed fountains of molten rock and smoke oozing from fissures in the ground across a large region near the town of Grindavik.
The volcano erupted early on Sunday north of the town, which had just been evacuated for the second time since November due to worries of an outbreak amid a swarm of seismic activity, authorities said.
Authorities have constructed earth and rock barriers in recent weeks to try to keep lava from reaching Grindavik, around 40 kilometers (25 miles) southwest of the capital Reykjavik, but the current eruption appears to have penetrated the town’s defenses.
“According to the first images from the Coast Guard’s surveillance flight, a crack has opened on both sides of the defences that have begun to be built north of Grindavik,” the Icelandic Meteorological Office IMO informed.
It was the second volcanic eruption on the Reykjanes peninsula in southwest Iceland in less than a month, and the sixth since 2021.
Last month, an eruption began in the Svartsengi volcanic system on December 18, following the entire evacuation of Grindavik’s 4,000 people a month prior and the closure of the Blue Lagoon, a famous tourist attraction.