"There are no plans to reduce the warning status. Based on experience, Merapi becomes calm before it erupts," said Ratdo Mopurbo, one scientist monitoring the volcano on the main island of Java.
Officials ordered everyone within an 8km (five-mile) radius to evacuate on Saturday when the mountain began belching clouds of ash and smoke, and streams of hot lava rolled down its slopes.
Scientists say the highest alert is still in place for the country's most active volcano, even though lava flows and emissions have reduced over the last 24 hours.
"There are no plans to reduce the warning status. Based on experience, Merapi becomes calm before it erupts," said Ratdo Mopurbo, one scientist monitoring the volcano on the main island of Java.
Another warned of the potential disaster posed by a vast build-up of lava at Merapi's summit.
"The villagers are in a very dangerous situation because the mountain is so unpredictable," he said.
Local police, however, say only a small number of elderly people and children have complied with the order to go.
Violent history
Vulcanologists have been monitoring Merapi for weeks but have yet to classify its month-long rumblings, however violent, as an eruption.
In November 1994 it erupted again without warning, killing more than 60 people.
Four years later thousands were forced to flee their homes as it spewed ash and toxic gas.
Ash cloud
Although there have been no casualties so far, Merapi has already sparked health fears across a wide area.
Ash rain - which can cause respiratory illnesses, skin diseases, diarrhoea and severe eye infections - is reported to have fallen on cities as far as 100km away.
Thousands of masks have been distributed to people living near the 2,968 metre (9,794-foot) volcano.
Merapi is one of some 500 volcanoes in Indonesia, at least 129 of which are considered active.
It lies in one of Indonesia's most densely populated regions, and is only a few kilometres from the ancient city of Yogyakarta, an area now home to two million people.
The city remains unaffected so far.
Indonesia is near the "Ring of Fire" - the circle around the Pacific Ocean on which lie most of the world's active volcanoes above sea level.