California's governor is asking the US federal government to help his state after it was hit by a seismic one-two in as many days.
More than 5,000 tremors, of varying strengths, have been recorded since the inital 6.4 magnitude quake. It was later followed by a 7.1 tremor.
Governor Gavin Newsom says there has been significant damage to critical infrastructure.
Our correspondent Rachel Silverman is in San Francisco. She tells Philippa Tolley that California is still being rattled by thousands of aftershocks.
