The volcano registered more than 30 tremors on Sunday and more than 200 in the past week, Subandriyo, from the Vulcanology Centre in Central Java, told AFP.

Vulcanologists have put the volcano on alert stage two, one level below ordering an evacuation and two below a full eruption.

"Its activity has increased, although it is not yet critical," Subandriyo said.

Thousands of residents living near the mountain were told last Thursday of the increased threat from the volcano.

Merapi, which has been rumbling intermittently over the past four years, looms above a plain located in the southern area of Central Java province, just north of the cultural city of Yogyakarta, home to more than 500,000 people.

Merapi's most deadly eruption occurred in 1930, when 1,369 people were killed. It also erupted in 1994, killing 66 people.

Indonesia sits on the "Pacific Rim of Fire" noted for its volcanic and seismic activity. The country has more than 100 active volcanoes.

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