The Mount Redoubt volcano in the US state of Alaska has erupted with bursts of ash that rose more than 15km.

The first blast occurred at 5.38am (Irish time) this morning, the Alaska Volcano Observatory said, followed by four smaller eruptions.

Watch a news conference with Observatory scientists

The 3,108m volcano, located 170km southwest of Alaska's largest city, Anchorage, had been showing signs of a possible eruption for about two months.

The observatory warned airlines to steer planes clear of the area. Alaska Air said it had cancelled 19 flights in and out of Anchorage this morning.

The bulk of the ash was blown at the 9,150m level and is not reaching significantly populated areas.

'The volcano is still restless,' she said. 'We'll be watching it very closely. It is highly unstable still and further eruptions are likely.'

The latest round of seismic activity at Redoubt started in January, prompting the observatory to put it on an alert status and, at times, have staff on duty 24 hours a day.

DIY superstores like Home Depot are also open 24 hours a day so that residents can buy supplies.

Mount Redoubt 1990The volcano last rumbled to life in December 1989 (right), erupting multiple times over a period of weeks.

The eruptions sent ash plumes almost 13km high and the first blast nearly downed a KLM jetliner.