As Kilauea simmered on Friday, oozing lava from 22 fissures on its eastern flank, residents of Pahoa on the Big Island hunkered down in shelters and waited for an expected resumption of major eruptions.

The first evacuations came before dawn on May 3 when the volcano began its current cycle of eruptions and earthquakes.

Kilauea spewed ash nearly 9km into the sky on Thursday in what scientists warned could be the first in a string of even more violent explosive eruptions.

Residents were warned to take shelter from the ash as toxic gas levels spiked in a small southeast area where lava has burst from the ground during the two-week eruption.

The mouth of the summit crater vent has nearly tripled in size during the past couple of days from about 5ha to 14ha, USGS geophysicist Mike Poland says.

While this widening coincided with back-to-back explosive, steam-driven eruptions from the crater this week, Poland says the enlargement was caused primarily by the interior walls of the crater vent collapsing as the magma continues to drop through the throat of the volcano.

Geologists say it remains unlikely Kilauea will have a massive eruption like that of 1790, which killed dozens of people.

Kilauea's falling lava lake has likely descended to a level at or below the water table, allowing water to run on to the top of its lava column and create steam-driven blasts, they said.

A spike in toxic sulphur dioxide gas levels has closed schools around the town of Pahoa, 40km east of the volcano, where lava from giant cracks has destroyed 40 homes and other structures and forced about 2000 residents to flee.

A change in wind direction caused volcanic gas to drift northwest towards Pahoa, prompting National Guard troops to don gas masks at a nearby road intersection.

Australian Associated Press