Hundreds of deep tremors shook one of Indonesia's deadliest volcanos Friday, prompting the evacuation of thousands of people because the mountain could erupt at any time, a government official said.

Tenfold the normal number of tremors rattled Mount Kelud and its crater lake was the hottest since the area was put on high alert last month, said Surono, a senior government volcanologist who goes by a single name.

"Kelud is entering its critical phase," Surono said in a telephone interview.

An underground reservoir of magma is pushing up to the surface, but is being blocked by sediment from the 1990 eruption, said scientist Mohammad Hendrasto. That intense pressure could result in "the most horrifying eruption in Kelud's history," he said.

Meanwhile, a second volcano in the seismically active nation, Mount Anak Krakatau, spewed up lava for the first time since it started erupting last week, said volcanologist Cahaya, who goes by one name. A major eruption at the volcano, however, wasn't expected.

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 when the peak was put at its highest alert level more than two weeks ago, 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.

Sugeng Ruwanto said many villagers believed a local myth stating that if they stayed at home without switching indoor lights on or speaking in a loud voice then the mountain would not erupt.

Along with hundreds of other people, Ruwanto remained in Anyar village, some three miles from the crater of Kelud.

Indonesia, which has around 100 active volcanos spread across 17,500 islands, sits on the so-called "Ring of Fire" — a series of fault lines stretching from the Western Hemisphere through Japan and Southeast Asia.