One of Indonesia's deadliest volcanos began erupting Saturday, but there was no visual confirmation of activity because the peak was cloaked in dense fog, a senior government volcanologist said.

Seismic readings showed Mt. Kelud was erupting, said Saut Simatupang, a leading scientist with Indonesia's Volcanology Center. The mountain was put on high alert several weeks ago and tens of thousands of people have been forced to evacuate the area.

Another volcanologist who has been watching Kelud from a viewing station, Umar Rosadi, said the crater did not appear to have spewed lava or ash.

Panicked residents fled the mountain's slopes and monitors were ordered to abandoned their posts Saturday, witnesses said.

Hundreds of underground tremors have been shaking the area and the temperature of its crater lake has reached the highest level since the mountain was put on high alert several weeks ago.

In 1990, Mt. Kelud killed more than 30 people and injured hundreds. In 1919, a powerful explosion that could be heard hundreds of miles away destroyed dozens of villages and killed at least 5,160.

On Thursday, police went door-to-door and used megaphones to order villagers to flee to tent camps.

More than 100,000 people living in areas considered to be at risk were ordered from their homes last month, but most never left or have since returned to their homes, officials say.

Some of those who stayed behind were asked to sign a statement saying they would not seek compensation funds if they were injured or lost family members due to an eruption, said local community leader chief Susiadi, who also goes by a single name.