Jakarta: Indonesia's most active volcano, Mount Merapi, has erupted, sending a column of volcanic materials as high as 5500 meters into the sky, forcing evacuations and the closure of an airport.

Disaster Mitigation Agency spokesman Sutopo Purwo Nugroho said the eruption on Friday morning happened suddenly and was accompanied by a rumbling sound with medium to strong pressure.

There were no immediate reports of casualties, and local authorities have asked people living within 5 kilometers of the crater to evacuate.

He said that 120 people who had been hiking up Merapi were safe.

The airport in Yogyakarta, the nearest big city to the volcano, shut because of the threat from the ash, the state-owned aviation agency AirNav said in a statement.