Indonesia`s Mt. Kelud critical, may erupt - scientist
"Kelud is in a critical phase. It could erupt now," Surono, head of Indonesia's centre for Vulcanology and Geological Hazard Mitigation, told Reuters by telephone from the capital Jakarta.
On Thursday, another official said there had been more than 600 hundred tremors recorded and hundreds of residents had evacuated.
Thousands of people had already left from a 10-km (6-mile) zone around Kelud since the alert was first raised, but many had returned home, fearing for the safety of their possessions.
Umar Rosadi, a vulcanologist at the volcano monitoring post near Kelud, said on Thursday that magma was 700 metres (2,296 feet) below the crater and could shoot out if it had enough energy.