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 steam-driven blasts.
Kilauea is one of the most active volcanoes in the world and one of five on Hawaii's Big Island.
Aloha Junction Bed and Breakfast owner Robert Hughes says there were a few small earthquakes Wednesday but he heard nothing Thursday when the volcano erupted.
The state Civil Defense agency said the plume was drifting northeast and warned residents to shelter in place.
An ash plume Wednesday rose roughly 12,000 feet into the air, and on Tuesday, the USGS issued a red alert, which means a major eruption is imminent or underway and ash could affect air traffic.
Mike Poland, a geophysicist with the US Geological Survey, confirmed the explosion and said people needed to shelter in place.
The Hawaiian Volcano Observatory says the strongest shaking was recorded around 8:30 a.m., measured as a 4.4-magnitude natural disaster, and earthquakes are expected to continue.More news: EU Suing France, UK and Germany over Air Pollution Levels
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The explosion at the mountain summit came shortly after 4 a.m. following two weeks of volcanic activity that sent lava flows into neighborhoods and destroyed at least 26 homes.
The 4:15 a.m. (10:15 a.m. ET) blast that sent ash and smoke almost six miles into the atmosphere was followed by other emissions of up to 12,000 feet, the U.S. Geological Survey said in a statement. The wind will carry the plume towards the south-east.
Since a new zone of Mount Kilauea began erupting nearly two weeks ago, lava has wrecked dozens of homes and forced hundreds of people to be evacuated.
Communities a kilometre or two away may be showered by pea-size fragments or dusted with nontoxic ash, they said.
The news comes amid worsening air quality conditions on the Big Island, and as civil defense authorities continue to respond to Kilauea's ongoing eruptions in lower Puna, where thousands of people remain under mandatory evacuation orders. Hawaiian Volcano Observatory and Hawaii National Park staff members were evacuated ahead of the eruption, according to the USGS.