The lava crossed onto the Puna Geothermal Venture (PGV) on Saturday evening local time, according to the US Geological Survey, having destroyed dozens of nearby houses in the past few days.

Since Hawaii's Kilauea volcano began a once-in-a-century-scale eruption May 3, authorities have shutdown the plant, removed 227,000 litres 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 40km east underground, bursting out of about two dozen giant cracks or fissures near the plant.

Hawaii Governor David Ige has said the PGV wells are stable.

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 sulfide and other gases should wells be ruptured.

Residents have complained of health hazards from emissions from the plant since it went online in 1989 and 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 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.

In just the past 24 hours there were between 250 and 270 earthquakes at Kilauea's summit, with four explosions on Saturday sending ash as high as 4.5km in the air, said Stovall and National Weather Service meteorologist John Bravender.

US Marine Corp and National Guard helicopters are on standby for an air evacuation in the event fissure activity cuts off Highway 130, the last exit route for up to 1000 coastal residents. Cracks in the highway have yet to emit hydrogen sulfide gas which would indicate magma was rising towards the surface, Stovall said.

Australian Associated Press