The Icelandic Meteorological Office (IMO) said in a statement that although the eruption had decreased significantly, it was still too early to say that it was ending.
The Blue Lagoon luxury geothermal spa, a tourist attraction, was closed to the public after lava covered its main access road, although the giant outdoor pool itself was unscathed, a Reuters eyewitness said after briefly being allowed to visit.
The temperature in the area stood at 17.6 Fahrenheit (minus 8 degrees Celsius) early on Friday.
Some 20 people had worked overnight to restore hot water via an emergency pipeline that was already under construction, utility HS Orka said in a post on Facebook.
It was the third eruption in the area, just south of the capital Reykjavik, since December.
