California confirms second US coronavirus case of unknown origin

California health officials on Friday confirmed a second suspected US case of the new coronavirus transmitted to a person who did not travel overseas or come in contact with anyone known to be ill, prompting fears of a possible outbreak in the country.

"This new case indicates that there is evidence of community transmission but the extent is still not clear," said Sara Cody, director of public health for Santa Clara County, the heart of Silicon Valley where tech giants like Apple and Google are based.

"What we know now is that the virus is here, present at some level, but we still don't know to what degree," she added.

The patient in the second case of community spread of COVID-19, as the virus is called, is an adult woman with chronic health issues. She is being treated at a local hospital.

Cody said the woman's doctor had reached out to health officials on Wednesday evening, concerned she may have contracted the virus. Authorities have identified dozens of people the woman had come in contact with and they were quarantined in their homes.

"An important priority... for us is to conduct public health surveillance to determine the extent of what's happening," Cody said.

"We need to begin implementing additional measures to prevent the spread of novel coronavirus or at least slow it down as much as possible."