The alert level for Pavlof volcano has been raised from "Watch" to "Warning" by Alaskan officials after an ash cloud reached more than 20,000ft high and 50 miles east of the volcano's peak.
"The low-level eruption of Pavlof has escalated," officials announced as the aviation colour code was raised to "Red".
Campers have reported lava coming out of the northeast side of the volcano, John Power, the observatory's chief scientist told the Anchorage News Daily.
"Elevated surface temperatures were detected at the summit of Pavlof volcano in satellite imagery this morning suggesting that the volcano is experiencing a low-level eruption with lava at the surface," the Alaska Volcano Observatory (AVO) reported.
"Recent satellite images show a plume extending over 80 km east of the volcano," the AVO statement continued.
Some weak seismic activity has been detected and some "small explosion signals" have been recorded by an infrasound sensor.
Scientist Robert McGinsey told the Associated Press that the eruption could last for "hours, days or weeks."
Pavlof volcano stands at 8,262ft and is located 625 miles southwest of Anchorage on the Alaska Peninsula.
Since 1980, dozens of eruptions have emanated from the volcano which is one of Alaska's most active.
There are currently no reports of flight cancellations following the heightened eruption warning.