The 3,078-meter (10,157 feet) Mount Ciremai near the town of Kuningan in West Java began "a new phase or state of activity" last week, signaled by a small sequence of earth tremors, said Maman Sukirman, an official with the Mount Ciremai monitoring post.
Some 6,000 residents in 20 villages are living surrounding the volcano, the highest in West Java province, Sukirman told AFP.
"Villagers living near the volcano have felt minor but constant tremors since last week. They have not yet been evacuated because the volcano's activity is still relatively non-threatening," he said by telephone from his post, some 10 kilometers (6.2 miles) west of the crater.
Authorities have issued an "alert" status and are monitoring the volcano around the clock, he said.
Mount Ciremai, some 200 kilometers southeast of Jakarta, last erupted in
The Indonesian archipelago has some 127 active volcanos along what is known as the Pacific Ring of Fire.