The eruption does not immediately threaten the peninsula's settlements, but volcanic ash, consisting of magma particles with a diameter of up to 2 millimeters (.078 inches), can poison land and water. Ash emissions and trails can also present a danger to aircraft.
Alexei Ozerov, a leading researcher at the Russian Academy of Sciences Volcanology and Seismology Institute's Far Eastern department, said that at about 11 a.m. Moscow time (8 a.m. GMT), experts at the institute's monitoring station observed a pulsating glow above the giant volcano's crater, indicating that fresh magma was rising to the surface.
The ash trail from the eruption has already spread 35 kilometers (21 miles) to the southwest of Klyuchevskoi.
Volcanologists predicted the volcano's imminent eruption three weeks ago.
Klyuchevskoi's last eruption took place in January-May 2005.