The explosion sent large blocks to distances up to a kilometer from the dome and pyroclastic flow travelled down Gages Valley and into Plymouth where buildings there were set alight.
The fire last for several hours afterwards, officials said.

The explosion and pyroclastic flow also generated ash columns and these were accompanied by lightning strikes. Scientists say the hazard level around the area remains at level three or dangerous.
Plymouth, the former capital city, was abandoned when the volcano erupted in 1997 and killed 19 people. The area has been a ghost town since.