A volcano in south-western Iceland has erupted for the third time since December, sending jets of lava into the sky and triggering the evacuation of the Blue Lagoon spa, one of the island nation’s biggest tourist attractions.

The eruption began at about 0600 GMT along a three-kilometre (nearly two-mile) fissure northeast of Mount Sylingarfell, the Icelandic Meteorological Office said.

Several communities on the Reykjanes Peninsula were cut off from heat and hot water after a river of lava engulfed a supply pipeline.

The eruption site is about four kilometres (two-and-a-half miles) north-east of Grindavik, a coastal town of 3,800 people that was evacuated before a previous eruption on December 18.

The Meteorological Office said there was no immediate threat to the town on Thursday.

Civil Defence officials said that no-one was believed to be in Grindavik at the time of the new eruption.

A view of lava near to the road to Grindavik close to the exit for the Blue Lagoon, in Grindavik, Iceland
Lava near to the road to Grindavik close to the exit for the Blue Lagoon, in Grindavik, Iceland (Marco Di Marco/AP)

“They weren’t meant to be, and we don’t know about any,” Vioir Reynisson, the head of Iceland’s Civil Defence, told national broadcaster RUV.

The Civil Defence agency said that lava was heading for a pipe that supplies communities on the peninsula with hot water from the Svartsengi geothermal plant.

Authorities asked people to use hot water sparingly, as workers rushed to lay an underground water pipe as a back-up.

The nearby Blue Lagoon thermal spa was closed when the eruption began and all the guests were safely evacuated, RUV said.

A stream of steaming lava later spread across the exit road from the spa.

People look at the volcano erupting north of Grindavik, Iceland
People look at the volcano erupting north of Grindavik, Iceland (Marco Di Marco/AP)

The Icelandic Met Office earlier this week warned of a possible eruption after monitoring a build-up of subsurface magma for the past three weeks.

The amount of magma or semi-molten rock that had accumulated was similar to the amount released during an eruption in January.

Hundreds of small earthquakes had been measured in the area since last Friday, capped by a burst of intense seismic activity about half an hour before the latest eruption began.

Dramatic video from Iceland’s coast guard shows fountains of lava soaring more than 50 metres (165ft) into the darkened skies.

A plume of vapour is rising about three kilometres (one-and-a-half miles) above the volcano.

This is the third eruption since December of a volcanic system on the Reykjanes Peninsula, which is home to Keflavik, Iceland’s main airport.

A volcano erupting north of Grindavik, Iceland
A volcano erupting north of Grindavik (Marco Di Marco/AP)

There was no disruption reported to the airport on Thursday.

Iceland, which sits above a volcanic hot spot in the North Atlantic, averages an eruption every four to five years.

The most disruptive in recent times was the 2010 eruption of the Eyjafjallajokull volcano, which spewed huge clouds of ash into the atmosphere and led to widespread airspace closures over Europe.

Grindavik, about 50 kilometres (30 miles) south-west of Iceland’s capital Reykjavik, was evacuated in November when the Svartsengi volcanic system awakened after almost 800 years with a series of earthquakes that opened large cracks in the earth between the town and Sylingarfell, a small mountain to the north.

The volcano eventually erupted on December 18, sending lava flowing away from Grindavik.

A second eruption that began on January 14 sent lava towards the town.

Defensive walls that had been bolstered since the first eruption stopped some of the flow, but several buildings were consumed by the semi-molten flow.

No confirmed deaths have been reported, but a workman is missing after falling into a fissure opened by the volcano.

Both the previous eruptions lasted only a matter of days, but they signal what Icelandic President Gudni Th. Johannesson called “a daunting period of upheaval” on the Reykjanes Peninsula, one of the most densely populated parts of Iceland.

According to volcanologist Dave McGarvie, who has worked extensively in Iceland, it’s unclear whether the residents of Grindavik will ever be able to return permanently.

“I think at the moment there is the resignation, the stoical resignation, that, for the foreseeable future, the town is basically uninhabitable,” he said.

He added that after centuries of quiet, “people thought this area was fairly safe.”

“It’s been a bit of a shock that it has come back to life,” he said.

“Evidence that we gathered only quite recently is that eruptions could go on for decades, if not centuries, sporadically in this particular peninsula.”