Mike Poland, a geophysicist with the US Geological Survey, confirmed the explosion on Thursday.
It comes after more than a dozen fissures recently opened miles to the east of the crater and spewed lava into neighbourhoods.
Those areas were evacuated as lava destroyed at least 26 homes and 10 other structures.
The crater sits within the Hawaii Volcanoes National Park, which has been closed since May 11.
Officials have said they did not expect the explosion to be deadly as long as people remained out of the park.
Kilauea is one of the world's most active volcanoes.
An eruption in 1924 killed one person and sent rocks, ash and dust into the air for 17 days.
Scientists warned on May 9 that a drop in the lava lake at the summit might create conditions for an explosion that could fling ash and boulders the size of fridges into the air.
Scientists predicted it would mostly release trapped steam from flash-heated groundwater released as though it was a kitchen pressure cooker.
Kilauea volcano has been erupting continuously since 1983.
It's one of five volcanoes that comprise the Big Island of Hawaii, and the only one currently erupting.
Residents who live in a nearby town reported light amounts of ash after the eruption.
The volcano on the Big Island exploded at about 6am. Mr Poland said the explosion probably only lasted a few minutes.
Mr Poland said accumulations are minimal, and it will likely be trace amounts near the volcano and on a nearby town, named Volcano.
About two hours later, Mr Poland said the webcam view showed a dusty plume rising from the summit. It looked like it was a steam and ash plume.