The nearby geothermal spa Blue Lagoon had closed on Thursday, it said.
The previous eruption in the area started on Jan 14 and lasted roughly two days, with lava flows reaching the outskirts of the Grindavik fishing town, whose nearly 4,000 inhabitants had been evacuated, setting some houses alight.
Thursday’s eruption took place some way from Grindavik and was unlikely to pose a direct threat to the town, Icelandic geophysicist Ari Trausti Gudmundsson told Reuters.
“But it could pose some threat to the road to Grindavik and it could pose some threat to the power plant and even to the Blue Lagoon,” he said, adding that the risk depended on how much lava ultimately flowed from the ground.
The Reykjanes outbreaks are so-called fissure eruptions which are often referred to as Icelandic-type. They do not usually result in large explosions or significant production of ash dispersed into the stratosphere.
Reykjavik’s international Keflavik airport was open and operating “in the usual way”, airport operator Isavia said on its website.