The volcano has started to "spew ash and lava", the state-owned TASS news agency reported, citing the Institute of Volcanology and Seismology of the Far Eastern Branch of the Russian Academy of Sciences.

"The eruption of the Shiveluch volcano has begun... According to visual evaluations, the ash column is rising as high as 8 kilometres above the sea level," the report quoted scientists as saying.

Earlier on Saturday night (local time), a 7.0-magnitude earthquake jolted a sea area off the east coast of Kamchatka.

The epicentre was monitored at 52.8 degrees north latitude and 160.15 degrees east longitude. The quake struck at a depth of 50 km, according to a report issued by the China Earthquake Networks Center.

The US National Tsunami Warning Center had initially issued a tsunami threat, but later said the threat had passed. The Russian Emergencies Ministry had not issued any tsunami warning.

The earthquake was followed by a series of aftershocks in the Pacific Ocean off Kamchatka, measuring between 3.9 and 5.0. Most of them were not felt on the land, TASS reported, citing the ministry.