Lava from Hawaii's erupting Kilauea volcano has covered a potentially explosive well at a geothermal power station and threatened another, after flowing onto the site, officials say.
The Hawaii Civil Defence Agency said the wells "are stable and secure," and Hawaii Governor David Ige said that the plant was "sufficiently safe" from the lava that has ploughed through backyards and streets and burned dozens of homes.
But lava has never engulfed a geothermal plant anywhere in the world and the potential threat is untested, according to the head of the state's emergency management agency.
Local residents fear an explosive emission of deadly hydrogen sulphide and other gases should wells be ruptured. The molten rock was expected to continue to flow across the Puna Geothermal Venture (PGV) facility, according to the US Geological Survey.
Since Hawaii's Kilauea volcano began a once-in-a-century-scale eruption on May 3, authorities have shut down the plant, removed 60,000 gallons of flammable liquid, and deactivated wells that tap into steam and gas deep in the Earth's core.
Magma has drained from Kilauea's summit lava lake and flowed around 40 km east underground, bursting out of about two dozen giant cracks or fissures near the plant.
Residents have complained of health hazards from plant emissions since it went online in 1989. PGV has been the target of lawsuits challenging its location on the flank of one of the world's most active volcanoes.
The Israeli-owned 38 megawatt plant typically provides around 25 per cent of electricity on the Big Island, according to local power utility Hawaii Electric Light.
Operator Ormat Technologies Inc last week said there was no above-ground damage to the plant, but it would have to wait until the situation stabilised to assess the impact of earthquakes and subterranean lava flows on the wells.
Over the weekend, there were more than 250 earthquakes at Kilauea's summit, with four explosions on Saturday sending ash as high as 4500 metres, officials said.
Winds are set to shift on Monday and Tuesday, causing higher concentrations of ash and volcanic smog that will spread west and northwest to affect more populated areas, said National Weather Service meteorologist John Bravender.
US Marine Corps and National Guard helicopters are on standby for an air evacuation if fissure activity cuts off Highway 130, the last exit route for up to 1000 coastal residents.
