GAMBAR, Indonesia, Nov 4 (Reuters) Indonesia's Mount Kelud volcano spewed ash today 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 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.
Officials at the vulcanology centre said on Saturday that the volcano had erupted while hidden by heavy cloud cover, but later they said that an eruption had not in fact taken place.
The authorities have been monitoring the volcano for several weeks and raised its alert status to the highest level about two weeks ago as its activity increased and an eruption appeared imminent.
However, they have found it difficult to convince villagers in the area to move to shelters. Many of those who evacuated to shelters in the past two weeks later returned to their homes.
''I left my house for two days and nothing happened. The house was abandoned so I decided to go back,'' said Wiji, a pregnant mother.
Many villagers in this area are superstitious, believing that if they turn off the lights and do not speak ill or loudly, the spirit of the volcano will calm down.
Some scientists have suggested that hardened larva from previous eruptions could be blocking the release of magma, and warn this could burst out once sufficient energy has built up.
Indonesian officials were also closely monitoring three other volcanoes for increased activity.
Indonesia has the highest number of active volcanoes of any country, sitting on a belt of intense seismic activity known as the ''Pacific Ring of Fire''.
REUTERS ARB KP1503