Government agencies and aid groups have begun sending personnel and supplies to more than 60 evacuation points in Yogyakarta and Central Java provinces in anticipation of a mass evacuation.
Approximately 40,000 people live in the vicinity of the 2,914m mountain.
"Everybody, including the military and police, is ready to carry out an evacuation and secure the areas," Priyadi Kardono, a spokesman for the National Disaster Management Agency (BNPB), told IRIN on 26 October.
"The local government is much more prepared to deal with an eruption thanks to past experience and the predictability of the volcano's activity," he said.
One day earlier, volcanologists put areas within a 10km radius on red alert after Merapi showed increased activity, spewing lava down its southern slopes.
Kardono said 800 people living along its slopes and considered most vulnerable -children, elderly people and the disabled, from two villages - Kemiren and Kaliurang - in Magelang District had been moved to temporary shelters.
BNPB has sent a team of six people to conduct an assessment and deliver aid supplies, including 60 platoon tents, masks and 500 million rupiah in cash (US$56,000).
The Indonesian Red Cross (PMI) has distributed 3,000 masks, 750 blankets, 40 rolls of plastic sheeting and 25 family tents, said Ali Masyhar, an official with PMI's Central Java chapter.
Masyhar said four districts - Boyolali and Klaten in Central Java and Magelang and Sleman in Yogyakarta - were at risk in the event of an eruption. However, many residents were reluctant to leave their homes because they do not want to leave their crops and cattle unattended.
"They have gotten used to the situation and believe they know what to do in an event of an eruption," he said.
On 21 October PMI held a drill in Klaten attended by 400 people to prepare for a Merapi eruption, Masyhar said.
Two people were killed in Merapi's last eruption in 2006. A 1994 eruption killed 66 people. Its deadliest eruption on record occurred in 1930 when 1,370 people were killed.
In September this year, the Mount Sinabung volcano in North Sumatra Province, which had been dormant for more than 400 years, also erupted, forcing tens of thousands from their homes.
Meanwhile, news agencies reported that at least 23 people were killed and 167 missing after a tsunami, apparently triggered by a 7.5 magnitude earthquake on 25 October, near the Mentawai islands off the coast of Sumatra, swept away villages.
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This article was produced by IRIN News while it was part of the United Nations Office for the Coordination of Humanitarian Affairs. Please send queries on copyright or liability to the UN. For more information: https://shop.un.org/rights-permissions