Clouds of deadly hot ash, rock fragments and volcanic gas surged down Merapi's slopes yesterday, as activity at the towering mountain intensified to its highest level yet, officials and eyewitnesses said.
One of the eruptions sent an avalanche of debris and ash rolling almost 4km down the mountain's western flank, said Ratdomopurbo, the region's chief vulcanologist.
It was followed by several other huge explosions on the crater.
Some people who earlier refused to leave the danger zone fled yesterday in public minivans or trucks. Villages near the peak resembled ghost towns, with only a few young men to be seen. Houses, some dusted with ash, were deserted and shops closed.
"I am panicking this time," said Katimi, a mother of three who had taken refuge in a mosque earmarked as an evacuation point. "Merapi appears angry."
Scientists raised the alert status for Merapi on Saturday to the highest level after weeks of volcanic activity, and by Sunday more than 4,500 people living in villages closest to the crater or next to rivers that could provide paths for hot lava had been evacuated.
They are living in mosques, government buildings and schools.
Some 18,000 others who live lower down the slopes of the 3,000m mountain, which rises from the plains of Indonesia's densely populated Java, and were not considered to be in immediate danger as of late Sunday.
Police -- who said there were no reports of damage or injuries -- toured the danger zone yesterday, urging the last holdouts to leave.
But scores refused, saying they wanted to protect their land or livestock.
"This is nothing special," said 25-year-old Anto. "It all depends on how brave you are."
Merapi, which is one of 129 active volcanoes in Indonesia, sent out a searing cloud of gas that burned 60 people to death when it last erupted in 1994. About 1,300 people died in a 1930 eruption.
The deadly clouds of ash, gas and debris, known to vulcanologists as pyroclastic flows, are the biggest worry for emergency services, said Sugiono, one of the scientists on a team monitoring the volcano 24 hours a day.
He said a glowing dome of lava being formed by magma forced to the surface was poised to collapse and could a trigger a surge in the clouds.
Locals call the clouds "Wed-hus Gembel," or "shaggy sheep clouds," because they resemble tightly curled balls of wool as they avalanche down the mountain at speeds of more than 100kph.
"If you get stuck in them, then you have no chance," Sugiono said.
Many mystic beliefs are associated with the mountain, and some Javanese also believe increased activity at Merapi is a sign of impending political upheaval.
On Sunday, holy men burned incense and floated offerings of rice, fruit and vegetables in a river that runs down the volcano's slopes -- a special ceremony they believe will ward off an eruption.
Although most Indonesians are Muslim, many also follow animist beliefs and worship ancient spirits, especially in central Java province. Often at full moons, they trek to crater rims and throw in rice, jewelry and live animals to appease the volcano.
"All the things we are doing here are to try to make us safe," said Assize Ashore, an Islamic preacher who also took part in the ceremony. "Only Allah knows if Merapi will explode."
The belief that a volatile Merapi foreshadows political instability dates back centuries.