Indonesia's most active volcano, Mount Merapi, has erupted, sending a column of volcanic material and ash more than 18,000ft into the sky.

The sudden eruption was accompanied by a rumbling sound with medium to strong pressure, the Disaster Mitigation Agency said.

People living within around three miles of the crater were evacuated to barracks set up for the displaced, or left for other safe places.

There were no immediate reports of casualties.

The agency said Adi Sucipto airport in Yogyakarta was closed for about one hour due to the spread of volcanic ash.

The eruption did not raise the alert status of Merapi, which is at a normal level with no eruption expected in the foreseeable future.

The 9,737ft mountain between the Yogyakarta and Central Java provinces is the most active of 500 Indonesian volcanoes. Its last major eruption in 2010 killed 347 people and caused the evacuation of 20,000 villagers.

Indonesia, an archipelago of more than 250 million people, is prone to earthquakes and volcanic activity because it sits along the Pacific "Ring of Fire," a horseshoe-shaped series of fault lines.