A volcanic eruption in Alaska that sent a plume of ash and smoke high into the sky has forced a regional airline to cancel flights.

The Pavlof volcano, which has been spewing ash and lava for years, began erupting with new intensity this week, prompting scientists to issue their highest volcano warning in five years.

The red alert - meaning a hazardous eruption is imminent, under way or suspected - has since been downgraded to orange, indicating an increased potential for eruption or that an eruption is under way but poses limited hazards.

Airline PenAir said cancellations continued through Wednesday as the it continued monitoring activity hourly.

Pavlof is located in an uninhabited region, nearly 966km southwest of Anchorage.

The volcano lies below a route frequently used by jetliners flying between North America and Asia, but those planes
generally fly at elevations of 9,144 meters and would likely be unaffected by ash at lower elevations, the Alaska Volcano Observatory said.

According to geologist Game McGimsey, diffused ash from Pavlof continues to reach heights as high as 7,315 metres.

"The eruptive activity continues pretty strong," McGimsey said. "There is lava fountaining going on. It's very visible at night time from web cams." 

According to the National Geographic website, scientists had not detected increased seismic activity under the mountain before this recent eruption, although they did note through satellite data that temperatures at the top spiked.

The last red alert issued was in 2009, when Alaska's Mount Redoubt produced a series of eruptions that spewed ash 1,500 metres into the air.

With almost 40 historic eruptions, Pavlof is one of the most consistently active volcanoes in the Aleutian arc, according to the Alaska Volcano Observatory.

Source: Agencies