Just months ago, California was being praised for its response to the pandemic. But now, with a surge in cases, the most populous US state is now having to reverse its easing of lockdown restrictions.

Prof Robert Wachter, the chair of the department of medicine at the University of California, San Francisco, told the BBC's Newsday that the state's early successes in fighting the spread of coronavirus meant that it was "appropriate" to begin lifting restrictions.

"But I think people took that as the starting gun for changing behaviour too much. So yes, people were allowed to go out and around, but they were supposed to be wearing masks, they were supposed to be keeping their distance, they were supposed to be avoiding large crowds. And I think too many people got a little bit complacent."

"They saw the tragedies in New York and in Italy and in China and other places, but after three or four months I think people began to get the feeling that 'OK, those are problems that happened there, we have dodged the bullet here, we're going great'," Prof Wachter said, adding that the federal government's mixed messages on masks and preventative measures had added to the confusion.

"Younger people said it's time to go back to normal, and it's clearly not."

A woman wearing a face mask walks at Venice Beach during a heatwave amid the coronavirus pandemic