The Reykjanes volcano in south-west Iceland has erupted, spewing lava and smoke into the air, after weeks of intense earthquake activity, the country’s Meteorological Office says.

Fearing a significant outbreak on the Reykjanes peninsula, authorities last month evacuated the nearly 4000 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 on Tuesday (AEDT).

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Images and a live-stream 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 coast guard helicopter would soon be in the air to confirm the exact location and size of the eruption, the Met Office said.

Reykjavik’s international airport, which is nearby, remained open.

“At the moment, there are no disruptions to arrivals or departures at Keflavík Airport,” it said on its website.

There have been several eruptions in unpopulated areas of the Reykjanes peninsula in recent years, but the latest outbreak could pose a risk to the Grindavik town, authorities have said.

There have been thousands of earthquakes in the area in the past two months but the magnitudes had declined in recent weeks, leading some experts to think risk of an eruption had abated.

Reykjanes is a volcanic and seismic hot spot south-west of the Iceland capital Reykjavik.

In March 2021, lava fountains erupted spectacularly from a 500-750-metre-long fissure in the ground in the Fagradalsfjall volcanic system.

-AAP