Alaskan authorities were on alert Monday after the Mount Redoubt volcano erupted five times, spewing plumes of smoke and ash some 15 kilometers (nine miles) into the air and forcing flight cancellations.

The Alaska Volcano Observatory said there were no immediate reports of casualties or damage from the 3,100 meter (10,200-foot) volcano, located not far from Anchorage, Alaska's most populous city.

Weeks of eruptions can be expected, officials said, similar to Mount Redoubt's last major eruption, when the volcano belched on and off for some four months starting in December 1989.

The eruptions, which began late Sunday, have unleashed a cloud of ash reaching up to 18,200 meters (60,000 feet) above sea level, said Rick Wessels, a geophysicist at the observatory. The explosions were also "pretty good sized," he said.

Alaska Airlines canceled 19 flights out of the international airport in Anchorage, which lies some 160 kilometers (100 miles) northeast of the volcano, and residents of nearby towns have been warned to prepare for falling ash.

"We expect these activities to last for weeks," said Interior Secretary Ken Salazar, speaking with volcano experts on a conference call to reporters.

Salazar said that Alaska officials were monitoring the safety of local residents and that of air travelers. Some 20,000 passengers fly through the area "on any given day," Salazar said.

Officials are also monitoring the Drift River Oil Terminal, an oil storage site located on Redoubt Bay, just 32 kilometers (20 miles) northeast of the volcano.

When the volcano last erupted, lava that crashed into the Drift River triggered a flood that reached the oil terminal, which was briefly evacuated.

Police in Anchorage earlier distributed flyers warning of the danger of hot ash.

The volcano observatory, which monitors activity at the state's 44 volcanos, reported at least five powerful eruptions on Mount Redoubt, including the first late Sunday.

Staff have been on alert since the volcano first began rumbling again in January, but a 24-hour watch has now been resumed and a red alert warning has been posted, the observatory said.

Early Monday the prevailing winds were pushing the ash north to the upper Susitna Valley and Talkeetna, known as a starting point for mountaineers attempting to climb Mount McKinley, the highest peak in North America.

"The ash is moving north and missing the bulk of the population in south-central Alaska," said US Geological Survey volcano expert Tom Murray, warning that eruptions "could go on for weeks."

Murray confirmed that ash had landed 160 kilometers (100 miles) north of the volcano.

The National Weather Service issued an ash fall advisory for towns including Talkeetna and Willow, some 120 kilometers (75 miles) and 56 kilometers (35 miles) north of Anchorage respectively.

"People in the areas of ash fall should seal windows and doors," protect electronics and minimize driving, the NWS advisory read.

The ash still posed a danger to aviation.

Alaska Airlines said in a statement it canceled its flights "as a safety precaution related to the pattern of ash at altitude created by the eruption.

"The airline is monitoring the ash pattern on a continuous basis and hopes to resume flights later when it is safe to do so."

Its planes on the ground in Anchorage have been "serviced and wrapped in protective sealant," the airline added.

The last significant blast from Mount Redoubt began in December 1989. Ash from the volcanic cloud clogged the four engines of a KLM airlines Boeing 747 that was flying by.

The plane plummeted more than 3,000 meters (10,000 feet) before the pilot managed to restart the engines, land the plane in Anchorage and save all 231 passengers.

Augustine volcano, situated on an isolated island in Cook Bay on which Anchorage is nestled, erupted in January 2006 without causing any damage or casualties.

Officials at Elmendorf Air Force Base in Anchorage said they were coordinating their response with local authorities.

"We've taken prudent precautions and have sheltered some aircraft, but our mission continues," said 3rd Wing commander Colonel Thomas Bergeson in a statement.

Elmendorf is home to some 60 aircraft, including F-22 Raptors -- the most advanced fighter jets in the US arsenal -- and F-15 fighter jets.