Lava and hot gas clouds have begun erupting from an Indonesian volcano, threatening hundreds of people living in nearby villages, an official said on Monday.

Saut Simatupang, the head of Indonesia's Vulcanology Survey, said nearly 600 people had evacuated their homes in an area south-east of Mount Karangetang.

Simatupang said the alert status for the volcano was raised to maximum at the weekend after hot clouds started moving eastwards, posing a threat to hundreds of people.

The 1,827 meter (5,994 feet) peak, on the diving resort island of Siau off Sulawesi and 2,325 km (1,445 miles) north-east of the capital Jakarta, is one of Indonesia's most active volcanoes.

"At least hundreds of the 30,000 people living on the island are at grave risk," Simatupang said by telephone from his office in the city of Bandung.

"We have recommended evacuation for entire districts and we are pushing for the complete evacuation of at least two villages located 5 km (3 miles) from the volcano's crater."

Simatupang said he received reports saying lava had already spread more than 1 km down the volcano's slopes.

Another volcano 175 km south of Mount Karangetang has also been spewing ash and sending debris down its slopes.

But Simatupang said that Mount Soputan, which lies on the northern tip of the Sulawesi island, was no threat to nearby villages.

Indonesia has the highest number of active volcanoes of any country, sitting on a belt of intense volcanic and seismic activity known as the "Pacific Ring of Fire."