An explosive eruption sent ash spewing out nine kilometres into the air above Hawaii's Kilaueau volcano on Thursday and residents of the Big Island were warned to shelter in place as the plume engulfed a wide area, authorities said.

The explosion came after two weeks of volcanic activity and the opening of more than a dozen fissures east of the crater that spewed lava into neighbourhoods.

"Hawaiian Volcano Observatory reports that an Explosive Eruption at Kilauea's Summit has occurred," County of Hawaii Civil Defense said in a phone alert. "The resulting ash plume will cover the surrounding area. Shelter in place if you are in the path of the ash plume."

Geologists had warned explosive eruptions could begin once Kilauea's falling lava lake descended below the water table, allowing water to run on to the top of the lava column and create a steam-driven blasts.