Mount Sinabung, which has been erupting intermittently since September, goes in to overdrive and rains rocks down forcing thousands to flee homes.

Several thousand people left their homes overnight, taking the total number of those who have fled since the volcano rumbled to life to around 12,300, said the national disaster agency.

"People panicked last night as the eruption was accompanied by a loud thunderous sound and vibrations. Then it started raining down rocks," said local government official Robert Peranginangin.

"They ran helter-skelter out of their homes and cried for help."