"They have started suffering diarrhoea and respiratory problems. Many villagers need immediate medical help," said Irsal, field coordinator for the Indonesian Red Cross (PMI).
Irsal, who like many Indonesians goes by only one name, said the Red Cross had already distributed 8,500 masks to protect residents against the volcano's fumes.
"The number of displaced villagers is likely to increase and distribution of humanitarian assistance remains uneven," he said.
Heidi Hasibuan, a 36-year-old civil servant who fled to the provincial capital Medan, complained that help had been slow in coming, with little warning of the impending disaster.
"Many of us have not received assistance from the government, not even a mask, and I'm worried as the smog is very thick," he complained.
He said there had been no warning from the government. "We were not prepared," he said.
Dormant for 400 years, Mount Sinabung first erupted on 29 August; a day later, it erupted again, sending hot ash 2,000m into the air, according to the government-run Center for Volcanology and Geological Disaster Mitigation.
"Most villagers within the volcano's 6km radius have now been evacuated," Priyadi Kardono, a National Disaster Management Agency (BNPB) spokesman, told IRIN on 30 August.
"Under control"
However, according to the UN Office for the Coordination of Humanitarian Affairs (OCHA), this is a considerably low-impact event compared with other disasters that strike the country.
"At this point, the situation looks under control," Ignacio Leon-Garcia, OCHA head of office, said from Jakarta. "We have been in contact with local and central government and no international assistance has been requested."
Nevertheless, authorities are keeping a close watch on the situation.
"We have to be alert at a time like this," Surono, director of the Volcanology centre, who also goes by only one name, said.
According to Maplecroft's Natural Disasters Risk Index 2010, of 229 countries surveyed, Indonesia ranked second only to Bangladesh in terms of vulnerability to natural disasters.
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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