The plume of vapor and gas with a high gas content has stretched for 12 miles northeast of the volcano, the Kamchatka branch of the Geophysical Service of the Russian Academy of Sciences reported Monday.
The eruption has been given the "orange" color code of hazard to aviation, and could pose risks to small-scale aviation, ITAR-Tass reported.
The 10,121-foot volcano began erupting Nov. 27, ending a 36-year dormant period.
Experts predict the Plosky Tolbachik eruption could go on for four months and the lava field deposited so far by lava flowing from a crack on the southern slope covers more than 5 square miles.
There is no hazard to inhabited areas, they said.