Tens of thousands of people packed emergency shelters after a long-dormant volcano in western Indonesia spewed clouds of hot ash and smoke more than a mile into the air.
The eruption of Mount Sinabung put the region on the highest alert level, and some domestic flights had to be diverted because of poor visibility.
Villagers living along Sinabung's fertile slopes in North Sumatra province started heading down the 8,000ft volcano after it began rumbling during the weekend.
An explosion on Sunday was followed by a much more powerful blast on Monday, and the number of people who evacuated hit 30,000, with hastily abandoned homes and crops blanketed in grey ash. The air was thick with the smell of sulphur.
Two people died, but Priyadi Kardono of the National Disaster Management Agency said it was too early to say if the volcano was to blame.
Sinabung last erupted in 1600, and officials acknowledged they had not been monitoring the volcano because it had been dormant for so long.
"The nearest monitoring post to Sinabung is Mount Merapi - around 400 kilometres to the south east - so we were totally in the dark. We didn't know anything until it started rumbling," said Imam Simulingga, a government vulcanologist.
He noted that there are 129 active volcanoes to watch in Indonesia, which is spread across 17,500 islands and is prone to eruptions and earthquakes because of its location within the so-called "Ring of Fire" - a series of fault lines stretching from the western hemisphere through Japan and south-east Asia.
"We'll be watching it closely from now on," said Surono, another government vulcanologist, adding that because eruption patterns have not been observed, "we really have no idea what to expect."
"We don't know what set it off, how long it will continue or whether we should expect pyroclastic flows or more powerful eruptions," added Surono.