Authorities raised the alert for Mount Raung to one notch below the highest, but no evacuation has been ordered, the National Geological Agency chief said. "Residents have been told to remain calm and avoid activities within a 3-kilometre radius from the crater," said Surono, who like many Indonesians goes by one name. The 3,332-metre volcano erupted last year, with no human casualties.
Residents said they were prepared to evacuate if ordered to.
"We are worried after saw fire sparks last night," resident Nuriamah told Metro TV. Indonesia is home to more than 130 active volcanoes.
Mount Sinabung in North Sumatra province has been spewing searing as hand gas since early June, forcing more than 10,000 people to leave their villages for safer areas.