Merapi, which means "Mountain of Fire", typically has small eruptions every two to three years, and larger ones about once every 10 to 15 years.

Its last major eruption was in 1994, when 66 people were killed. It also spewed smoke and lava in 2001 but no major eruption followed.

Located about 400 kilometres (250 miles) east of Jakarta in Central Java province, it looms over the Kedu plain and provides rich, bountiful soils for the thousands of people living around it.

Merapi holds particular significance for the Javanese as it is one of four places where officials from the royal palaces of Java's Yogyakarta and Solo make annual offerings to placate the spirits of ancient Javanese mythology.

Superstitious Javanese believe that a volcano's eruption is the result of spirits being angered by not receiving sufficient offerings or by a disrespectful attitude among the people living on its slopes.

Traditional beliefs hold that Merapi will only erupt after certain omens, some of which appear in dreams, leaving many residents reluctant to leave without them becoming apparent.

A new lava dome has been rapidly forming at the peak of 2,914-metre (9,616-foot) Mount Merapi, growing 75 metres in two weeks. The volcano was put on "stand-by" status one month ago.

Scientists predict that the dome's collapse will spew red-hot lava as well as deadly nuees ardentes, a geological term for clouds of volcanic gases, ash, and dust, reaching temperatures up to 500 degrees Celsius (930 degrees Fahrenheit).

Local authorities in the four districts around the volcano have already banned climbing near Merapi's peak, halted sand mining operations at its foot and warned people living higher on its slopes to be prepared for evacuation weeks ago.

Temporary shelters and vehicles have already been prepared for the evacuation, with several thousand people evacuating voluntarily but many returning to their homes.

Indonesia lies on the so-called Pacific Rim of Fire, where the meeting of continental plates causes frequent seismic and volcanic activity. The nation is home to more than 120 active volcanoes.

In August 1883, the biggest natural phenomenon ever seen on earth took place when after lying dormant for 300 years Indonesia's Krakatoa volcano burst to life, showering debris on Java and Sumatra islands and killing about 36,000 people.

The noise of the eruption reached Australia and territories located more than 4,000 kilometers away, while waves reaching up to 40 metres laid to waste nearby islands and were felt as far away as the English Channel.

Volcanic activity is still high, however, with tremors continuing and a lava dome, created by lava oozing through cracks, emerging from the crater like an "island" and continuing to expand.

"Lava is constantly shooting out of the crater. We recommend people keep a distance since there is always the danger of lava material catapulting far from the crater," volcanologist Agus Budianto told AFP.

"Amazing visuals can be seen from our CCTV (closed-circuit television)... The island is now 250 metres (yards) in diameter and stands 120 metres above the lake surface," he added.

Residents are being warned to stay at least three kilometres (two miles) from the crater. The danger zone was a 10-kilometre radius around the crater when the volcano was on its top alert, forcing the evacuation of thousands of people who have since returned home.

Smoke plumed up to two kilometres out of Mount Kelut on Sunday afternoon and ash covered a number of villages around the volcano.

"We have not made our own observations, but we heard reports of ash rain in several surrounding villages," volcanologist Jajang said from a monitoring post near the nearby town of Kediri.

Several volcanoes in Indonesia, which sits on the Pacific "Ring of Fire" where continental plates collide, have roared to life in recent weeks.

The archipelagic nation is home to about 130 active volcanoes, including 21 on Java.