More than 3,000 villagers have fled the area around a volcano in eastern Indonesia after it started blasting out hot gas and lava, officials said.

Saut Simatupang, a senior volcanologist, told Reuters the alert status for Mount Karangetan on Siau island was now at maximum.

"There is a hot gas cloud as far as 2.5 kilometres from the southern or southeastern parts of the volcano.

Since it (the cloud) is near to villagers' homes we have upgraded it to the top alert status," he said.

The official said there had been no casualties, but the lava flow was only 400 metres away from some villagers' homes.