(Reuters) - Indonesia's Mount Kelud volcano spewed ash on Sunday as clouds and fog turned daytime to dusk, sharply reducing visibility in the area.
A top official said the volcano had spewed ash about 500 metres into the air, a day after confusion over whether it had already started erupting.
An estimated 350,000 people live within 10 km ( 6 miles) of the volcano, which is about 90 km southwest of Surabaya, Indonesia's second-largest city and one of its busiest airports.
Kelud, also known as Kelut, means "sweeper" in Javanese, a reference to the fact that when it erupts, it sweeps away everything in its path.
When it last erupted in 1990 at least 30 people were killed, while about 5,000 died in 1919 when it spewed scalding water from its crater lake.
Umar Rosadi, a scientist monitoring the volcano, told Reuters there had been constant tremors from the 1,731 metre ( 5,700 foot) mountain in East Java, while the temperature of its crater lake had risen sharply.
"Technically, the condition today is more critical than yesterday," Rosadi said.
Saut Situmorang of Indonesia's Centre for Vulcanology and Geological Hazard Mitigation said volcanic ash rained down the northern slope of the volcano.