Jakarta, April 18 (IANS/DPA) Indonesian authorities have issued a tsunami warning and raised the alert for Mount Ruang to the highest level after the volcano near Sulawesi Island had multiple large eruptions over the past two days.

The heightened alert was issued late on Wednesday after the the 725-meter-high volcano had two large eruptions earlier in the day, spewing a column of ash 3,000 metres into the sky.

The head of Center for Volcanology and Geological Hazard Mitigation (PVMBG), Hendra Gunawan, said that authorities urged people living in the coastal area of neighboring Tagulandang island to remain alert for a potential tidal surge and tsunami which could be triggered by rockfalls from the volcano, which may collapse into the sea.

More than 800 people have been evacuated from two villages on Ruang island and authorities imposed an exclusion zone within a 6-kilometre radius of the crater, which extends to the south-western part of Tagulandang Island.

"Mount Ruang's eruption spewed ashfall, rocks and gravels that fell five kilometres away on the coastal areas of Tagulandang Island. Several residents were reported to have been hit by the falling rocks and stones," said Abdul Muhari, spokesman for the National Disaster Mitigation Agency.

Indonesian aviation authorities have issued a NOTAM ordering the closure of Sam Ratulangi airport in Manado, the provincial capital of North Sulawesi about 100 kilometres south of the volcano. The NOTAM has disrupted flights between Kuala Lumpur and major cities in Sabah and Sarawak, the Malaysian states in the neighbouring island of Borneo, which Indonesia shares with Malaysia and Brunei.

Mount Ruang last erupted in 2002, spewing out pyroclastic flows that damaged the land and local settlements.

The eruptions at Mount Ruang, located in North Sulawesi province, were preceded by volcanic earthquakes in recent days.

There are roughly 500 mountains that dot the Indonesian archipelago, of which 127 are active volcanoes and dozens of them have been showing signs of increased activity.