The Reykjanes volcano in south-west Iceland erupted on Monday, spewing lava and smoke into the air, after weeks of intense earthquake activity, the country's Meteorological Office said.
Fearing a significant outbreak on the Reykjanes peninsula, authorities last month evacuated the nearly 4,000 inhabitants of the fishing town of Grindavik and closed the nearby Blue Lagoon geothermal spa.
"Warning: Eruption has started north of Grindavik by Hagafell," the Met Office said on its website.
Images and a livestream broadcast by Reuters showed molten rock spewing like fountains from fissures in the ground, their bright-yellow and orange colours set in sharp contrast against the dark night sky.
Icelandic police said they had raised their alert level as a result of the outbreak and the country's civil defence warned the public not to approach the area while emergency personnel assessed the situation.
A coastguard helicopter was going to be in the air shortly to confirm the exact location and size of the eruption, the Met Office said.
Icelandic volcano erupts - in pictures
The eruption began about 10.17pm after a series of small earthquakes at about 9pm, the IMO said.
Reykjavik's international airport, which is near by, remained open.
"At the moment, there are no disruptions to arrivals or departures at Keflavík Airport," it said on its website.
The Reykjanes Peninsula in recent years had several eruptions in unpopulated areas, but the latest outbreak could pose a risk to the Grindavik, authorities have said.
The area had thousands of earthquakes in the past two months but the magnitudes had declined in recent weeks, leading some experts to think the risk of an eruption had abated.
Reykjanes is a volcanic and seismic hot-spot south-west of the capital Reykjavik.
In March 2021, lava fountains erupted spectacularly from a 500-750-metre-long fissure in the ground in the Fagradalsfjall volcanic system.
Iceland is home to 33 active volcano systems, the highest number in Europe.
