A volcano in southern Chile erupted with renewed vigor Tuesday, raining ash and lava over its surroundings and forcing a total evacuation in a 30-kilometer (19-mile) radius, the National Emergency Office said.

Emergency sirens sounded in the coastal region 1,300 kilometers (800 miles) south of Santiago, after the Chaiten volcano blasted out ash and cinders and generated lava and pyroclastic flows, four days after it awoke from a 300-year slumber.

"A maximum alert has been decreed," Jorge Munoz, the head of the National Emergency Office (ONEMI), told AFP in Santiago after the volcano blew its top at 8:45am (1245 GMT).

A government vulcanologist warned that the eruption was only at the beginning stage and that an explosive eruption was possible.

"There could be a major explosion that could collapse the volcano's cone," said Luis Lara of the National Geologic and Mining Service.

Chilean President Michelle Bachelet called for calm during the evacuation, which Interior Minister Edmundo Perez Yoma said affected a 30-kilometer (19 mile) radius.

"The volcano is exploding very strongly," Bachelet said.

Nearly 400 people from the surrounding area, including emergency workers and journalists, were put aboard two navy ships and other vessels and taken to safety.

People who refused to leave their homes were evacuated by force, a local radio said.

Only a contingency force of some 50 police and navy personnel were left in the town, the emergency office said.

Nearly all 4,000 residents of the coastal town of Chaiten, about 10 kilometers (six miles) from the 1,000-meter (3,280-foot) volcano, were evacuated over the weekend after the volcano began erupting on Friday, after being inactive for more than 300 years.

The landscape was dominated by the huge column of smoke and ash flowing kilometers (miles) into the sky from the volcano, leaving the town's buildings and streets covered with a thick blanket of ash, television images showed.

A blanket of ash extended from the volcano southward for scores of kilometers, slowly burying everything under 30 centimeters (12 inches) of ash that was turning cement-hard when mixed with rainfall.

In Futaleufu, a town 70 kilometers south of Chaiten, its 1,800 inhabitants were either being evacuated or fleeing over the border with Argentina just 15 kilometers to the east, after the town was buried in ash from the eruption.

A Chilean air force rescue team was dispatched to the area from Puerto Montt, about 200 kilometers (125 miles) to the north to send in new rescue teams.

"We are helping with the evacuation of Futaleufu," said a spokesman of the Argentine border police.

Carried by winds, the heavy ash from Chaiten was also raining down onto fields and valleys of Argentina, harming water supplies in the area.

Vulcanologist Lara said that the eruption could intensify.

"The conditions exist for something worse to happen," he said.

But he said the lava flows were not a big threat, because the lava is very dense.