Alaska volcano sparks aviation alert red

US authorities have raised their aviation warning to red following an eruption at Alaska's Bogoslof volcano.

An Alaska volcano that has been active for nearly six months has erupted again and authorities have raised an aviation alert to red.

The Alaska Volcano Observatory says Bogoslof volcano in the Aleutian Islands erupted for almost an hour on Sunday afternoon, sending a cloud of ash at least 10,670 metres.

The warning was raised to red, the highest level, following the eruption, with ash a potential threat to airliners operating between North America and Asia.