Another volcanic eruption has begun in south-west Iceland, forcing the evacuation of the famous geothermal Blue Lagoon spa and the small fishing town of Grindavik.

The new fissure opened up near Sundhnuksgigar on the Reykjanes peninsula, the fifth eruption in the area since December.

The Icelandic Meteorological Office (IMO) said the fissure was longer than 2.5km (1.5 miles) and was continuing to grow.

A state of emergency has been declared but air travel to and from Iceland was not expected to be affected.

Fannar Jónasson, the mayor of Grindavík, told state broadcaster RUV that he was worried about the amount of lava flowing towards the town, which was of a “much larger volume” than had been seen following recent eruptions.

Energy provider HS Veitur said power had been cut off to Grindavik as a precaution.

Three people had refused to leave the town, according to local media.

Officials later issued a statement to “strongly emphasise that all those who are in or near Grindavík leave the area and get to a safe distance”.

All but one road in and out of the town is now reported to be inaccessible.

Footage from the site of the eruption showed a wall of molten rock shooting up to a height of 50m, and huge plumes of ash covering most of the sky.

Natural history cinematographer, Benjamin Hardman, has been documenting Iceland’s volcanoes and was near the volcano when it erupted.

“It is totally surreal to be here today,” he told the BBC.

“This is a strange time on the Reykjanes peninsula.”

The Svartsengi power plant, which provides electricity and water to thousands of people on the peninsula, has also been evacuated.

Barriers have been built up around the facility, as well as Grindavik and the Blue Lagoon, to try to protect them from lava flows caused by the ongoing eruptions.

Keflavik international airport said it was operating as usual and did not expect to be affected.

Officials reported “intense earthquake activity” prior to Wednesday’s eruption.

Geophysicist Ari Trausti Gudmundsson said scientists had been expecting a new eruption for some time.

Most of the 4,000 residents of Grindavik were permanently evacuated in November, prior to the eruptions in December, January, February and March.

Lava flowed into its streets during the January eruption, engulfing three homes.

A few residents had since returned to live in neighbourhoods less at risk.

Iceland has 33 active volcano systems and sits over what is known as the Mid-Atlantic Ridge, the boundary between two of the largest tectonic plates on the planet.

The last time the Reykjanes Peninsula had a period of volcanic activity was 800 years ago – and the eruptions continued for decades.

This is now the eighth eruption since 2021, and scientists believe the area is entering a new volcanic era that could last for decades or even centuries.