The U.K. is on alert, with officials saying that “an earthquake of this magnitude would be devastating to coastal cities” in the British Isles.
has also confirmed an earthquake, but not an epicentre.
A preliminary magnitude-5.1 quake hit southern California, with dozens of aftershocks possible, including one at the same depth.
A magnitude-6.2 quake is expected in California later on Tuesday, and officials are urging people to stay home.
The US Geological Survey said there was no tsunami warning for the area, but the agency has advised people to seek shelter in place.
A small tsunami was recorded in southern California last month, the San Diego Union-Tribune reported.
The quake was located near an oil field.
A similar temblor hit near Mexico City in 2011.