US planes warned to avoid Alaska volcano

The US National Weather Service has warned planes to avoid airspace near an erupting Alaska volcano as it spews ash 9000 metres above sea level.

Winds were blowing ash from Pavlof Volcano to the west and southwest.

Pavlof began erupting, pushing lava out from a vent near its summit, on Wednesday.

On Friday, the ash cloud reached 4800m.

The eruption intensified at 6am local time on Saturday, sending the ash cloud higher, said Dave Schneider, a geophysicist at Alaska Volcano Observatory.

It's not clear how long this eruption will last, Schneider said.

Pavlof's eruptions may last for weeks or months with varying levels of intensity, he said.

Pavlof is Alaska's most active volcano and is located about 1005km southwest of Anchorage.

It has had more than 40 recorded eruptions, including earlier this year and last year.

It also lies along popular international air routes connecting Europe, North America and Asia.

The eruption has had little effect on people on the ground, with the closest community, Cold Bay, located 64km away.