Thousands of villagers fled Sunday after a volcano erupted on Indonesia's Sumatra island spewing rocks and red-hot ash onto surrounding villages, officials said.

Mount Sinabung in Karo district, North Sumatra province, erupted violently before dawn.

"More than 3,000 people have been evacuated from areas within a three-kilometre (two-mile) radius of the volcano, and they are all safe," Asren Nasution, the head of North Sumatra disaster agency, told AFP.

Five halls normally used for traditional cultural ceremonies had been converted into shelters for those displaced.

Sutopo Purwo Nugroho, national disaster agency spokesman, said 3,710 people had so far been evacuated.

Nugroho said it was second recent eruption of Sinabung. The volcano was dormant for nearly 100 years before erupting in August and September 2010, forcing about 12,000 people to flee.

Indonesia has dozens of active volcanoes and straddles major tectonic fault lines known as the "Ring of Fire" between the Pacific and Indian oceans.

Last month five people were killed and hundreds evacuated when a volcano on a tiny island in East Nusa Tenggara province erupted.

The country's most active volcano, Mount Merapi in central Java, killed more than 350 people in a series of violent eruptions in 2010.