Reports say at least eight soldiers killed by eruption on Jabal al-Tair island.
Another official said the number of volcanic quakes had dropped from around 500 on Tuesday to 61 on Wednesday morning, but said that did not mean an eruption could be ruled out.
“In fact, it may erupt in two or three days after there are quakes,” Simatupang, head of the vulcanological survey, said.
In Kampung Anyar, about 7km from the crater and within a zone deemed by authorities as dangerous, many villagers were at home.
Marsudi, a resident in the village, who evacuated and then returned to his home, said: “It’s not certain if Mount Kelud would ever go off. My parents and my siblings are at home at the moment. I’m going off to see some friends.
“Whenever we’re asked to evacuate, we will do so. But we came back simply because nothing happened,” he said.
When Kelud last erupted in 1990, around 30 people were killed and in 1919 about 5,000 died as it ejected scalding water from its crater lake.
Indonesia, which sits on a belt of intense seismic activity known as the Pacific Ring of Fire, has had a series of major volcanic eruptions over the centuries.