The quake was recorded at a depth of around 51km (32 miles), the European Mediterranean Seismological Centre said, according to media.
It struck at 8.10pm UK time according to USGS.
The US National Tsunami Warning Centre said there was a tsunami threat from the quake.
The tsunami warning said that waves "reaching 0.3m-1m" above tide level were possible for some coastal areas in Russia only.
It added that any possible tsunami or strong waves would likely hit around 8.30-9pm, UK time.
MNA