The volcanology agency has raised the alert level to the second highest, Xinhua news agency quoted a spokesman of the national disaster management agency as saying.
“All climbing activities, except for research purpose, is barred in the radius of three km from the crater.”
About 660 people have taken shelters to safer grounds, he added. “The number of evacuee keeps rising since last night,” he said.
The volcano, located in the main Java Island, witnessed eruptions four times since Monday with the latest one at 1.47 a.m. on Tuesday, sparking rains of ash in Sleman and Klaten districts, the spokesman said.
Mount Merapi is situated about 28 km north of Yogyakarta city which has a population of 2.4 million and thousands of people live on the flanks of the volcano.
The volcano has regularly erupted since 1948. In November 1994, pyroclastic flow from a large explosion killed 27 people, and another large eruption occurred in 2006.