A thick cloud covers the sky the provincial capital of Medan. The eruption occurred at 00.15 am (local time) and awoke thousands of shocked local residents who had been reassured by the local geophysics and meteorology agency that the volcanic mountain was not a serious threat. Now the authorities have issued a volcano warning.
Rising to 2,400 metres, Mount Sinabung erupted the last time in 1600. Since then, it has been inactive.
As the evacuation gets underway, the greatest problem is the thick ash cloud that hovers over the province’s largest cities.
Respiratory and eye problems are the greatest dangers for people.
Local officials now expect an “ash rain” that could disrupt air travel in the area and the capital.
The eruption could also become a serious obstacle for millions of people who are travelling from Indonesia’s capital Jakarta to their native villages to celebrate Idul Fitri, the end of Ramadan on 9 September.