A huge explosion rocked the Mount Pinatubo volcano Wednesday, spewing a towering plume of ash and steam that was visible 60 miles away in Manila. The remaining Americans at nearby Clark Air Base fled minutes after the eruption.
Roads were jammed as thousands of residents of the adjacent city of Angeles panicked as a grey-greenish mushroom cloud rose from the crater "like an atomic bomb."
The eruption _ the volcano's first in 600 years _ began at 8:51 a.m. (8:51 p.m. Tuesday EDT) with a tremendous explosion. Reporters at the scene said they heard three blasts and that the cloud blocked out the sun.
Raymundo Punongbayan, director of the Philippine Institute of Volcanology and Seismology, warned people within a 12-mile radius to flee.
"Even 30 kilometers (about 18 miles) _ to be safe," he said.
There were no immediate reports of casualties.
Threats of an eruption had prompted nearly 15,000 Americans to evacuate Clark last Monday. The evacuation virtually shut down one of the most important U.S. bases overseas. The base is about 10 miles east of the volcano.
Lt. Joy Sanchez, spokesman for the Philippine military's Clark Air Base Command, said the remaining 1,500 Americans and Filipino guards fled the base after a siren sounded at 9 a.m.
He said there was a huge traffic jam as residents of Angeles, a city of 300,000, tried to escape.
"The smoke is very thick like a dark mushroom in the sky," Gus Abelgas, a reporter for ABS-CBN television, said in a broadcast from Botolan, near the volcano's western slopes. "It's just like what we saw in Hiroshima."
Other reporters described panic in the area as people scampered for safety with their belongings and livestock.
In Angeles, church bells pealed to sound the alarm, and many people froze in their tracks with fear, then after a minute or two, they scampered for safety indoors.
"They were stunned by the eruption," reporter Bert Basa said by telephone from Angeles. "Their faces turned ashen, and it looked like their hair was standing on end."
About 19,000 Filipinos had been evacuated earlier from three provinces near the slopes of Mount Pinatubo. They were housed in about 25 makeshift evacuation centers outside the danger zone.
But there had been no general warning to residents of Angeles, where Clark is located. The city is 50 miles north of Manila.
Seismologist Julio Sabit said scientists were installing monitoring equipment on the mountain early Wednesday when they began to feel vibrations from the volcano.
"Most probably there will be more eruptions," he said. He said scientists saw "pyroclastic materials" _ a mixture of hot gas, rocks and other material flowing from the crater.
It was unclear whether this was the major eruption which scientists had been predicting at Mount Pinatubo. Two small eruptions occurred Sunday and Monday.
Most of the Americans stationed at Clark were transferred to the Subic Bay naval base and were expected to remain there until the danger was past.
Punongbayan said Tuesday that Clark was in the path of the volcanic flow from Mount Pinatubo during its last major eruption, in the 14th century.
Rollie Rimando, an Institute vulcanologist, said portions of Clark stand on rock formations formed during the last major eruption.
Rimando had said a major eruption could hurl debris and poisonous gases in a 12-mile radius, affecting both the base and parts of Angeles.
There are about 21 active and 200 dormant volcanoes in the Philippines. The last major eruption occurred in 1965, when the Taal volcano, about 50 miles south of Manila, exploded. About 200 people were killed.