Heavy rain overnight north of San Francisco, particularly in the Napa and Sonoma wine regions, caused several rivers to overflow, forcing the evacuation of at-risk neighborhoods, said Dale Chessey, an emergency services spokesman.

Six emergency shelters were opened in Napa and Sonoma, the local Red Cross chapter said.

A Napa city official quoted by the San Francisco Chronicle said at least 4,000 people had to be evacuated there and were spending New Year's Eve in Red Cross shelters.