Abandoned Kepuhargo village in Yogyakarta region is covered with volcanic ash from Mount Merapi. (Trisnadi/Associated Press)

The Indonesian military forced villagers off the slopes of the country's most volatile volcano as it erupted again on Saturday.

Mount Merapi on the island of Java, has been spewing hot ash and lava since Tuesday, killing at least 38 people and displacing about 40,000.

On Saturday, hot ash two kilometres high shot into the sky during a 21-minute eruption. The latest volcanic activity, which included 33 ash bursts, is blamed for two deaths.

More than 2,000 troops were called in to keep villagers clear of the mountain, except between 8 a.m. and 2 p.m. local time, when it appeared to be calm.

Government displacement camps were overflowing with refugees, including most of the 11,000 people who live on the mountain's fertile slopes.

They were told Saturday that with signs the danger level was climbing, they should expect to stay away from their homes for three more weeks.

Despite such warnings, many people have returned to their land to tend to their livestock and crops.

Aid slow in coming to tsunami survivors

Meanwhile, about 23,000 survivors of a tsunami that struck islands off the coast of Sumatra, hundreds of kilometres from Mount Merapi, are homeless and in desperate need of help.

Monday's earthquake and subsequent tsunami killed at least 413 people.

The death toll from the tsunami rose again Saturday as more bodies were found. Another 163 people were still missing and feared swept out to sea, officials said.

The wave that swept whole villages off their foundations when it hit was triggered by a 7.7-magnitude earthquake.

Aid and supplies have been slow in getting through to the most remote villages and islands.

Because of stormy weather and rough seas, government agencies on Friday were forced to pull back boats and helicopters that had been ferrying noodles, sardines and sleeping mats to the most distant corners of the Mentawai islands.

But military officials began bringing supplies to the hospital in Sikakap on Saturday, and about two dozen patients had been moved off the floor and onto camp stretcher beds.

With files from The Associated Press