The US Geological Survey said the eruption took place at 4.15am local time. Staff at the volcano observatory and the national park had previously been evacuated.
Since a new zone of Mount Kilauea began erupting almost two weeks ago, lava has wrecked dozens of homes and forced hundreds of people to be evacuated.
A red aviation code had already been issued - warning pilots to avoid the potentially damaging ash cloud.
The County of Hawaii Civil Defense warned in an alert the wind could carry the ash plume as far as Hilo, the Big Island's largest city and major tourism center.
"Protect yourself from ash fallout," it said.
USGS geologists and staff were evacuated from the summit shortly before the blast and a webcam showed a grey plume of ash and chunks of magma known as pyroclasts that showered the volcano's slopes.
National Guard troops donned gas masks to protect themselves from toxic sulfur dioxide gas at the intersection of highways 130 and 132, the main exit routes from the village of Pahoa, 25 miles (40 km) east of the volcano, where many of the ground fissures have erupted, a Reuters reporter in the village said.
Schools were closed in the area due to "elevated sulfur dioxide (SO2) levels," according to a phone alert from emergency authorities
The volcano has destroyed at least 37 homes and other structures in a small southeast area of the island where lava has oozed from fissures, forcing around 2,000 people to evacuate their homes.
The USGS had warned that an explosive eruption at Kilauea was becoming more likely as the volcano's lava lake was lowering.
This increases the risk of highly explosive steam-powered eruptions as the magma meets underground water.
Hawaii's emergency management agency advised people in the area affected by ash to stay in their homes if possible.
Kilauea is one of five active volcanoes on the island of Hawaii.
It is one of the most active volcanoes in the world and has been erupting continuously, though not explosively, for more than 30 years.
Its last explosive eruption took place in 1924.
Even before Thursday morning's explosive eruption, the ash plume from the volcano could be seen from the International Space Station.