A 6.6-magnitude earthquake hit southwestern Siberia in Russia on Tuesday, the U.S. Geological Survey said.

The epicentre of the quake, which hit at 10:21 a.m. ET, was 6.9 kilometres deep and about 96 kilometres east of Kyzyl, Russia and 336 kilometres northeast of Ulaangom, Mongolia, according to the USGS.

There was no immediate word on casualties or damage.

The severity of an earthquake can be expressed in terms of both intensity and magnitude, the USGS explains.

Earthquakes with a magnitude of about 2.0 or less on the Richter scale are usually called microearthquakes and are not commonly felt by people. Events with magnitudes of about 4.5 or greater — there are several thousand such shocks annually — are strong enough to be recorded by sensitive seismographs.

Great earthquakes, such as the 1964 Good Friday earthquake in Alaska, have magnitudes of 8.0 or higher. On average, one earthquake that size occurs somewhere in the world each year.