It's not clear how long the measures, which affect foreigners holding valid visas and residence permits, will remain in place. Exemptions will be made for diplomats and plane crews.

The government has put in place a strict regime of health checks, monitoring and quarantine in the hope that it can catch inbound cases before infections spread. A British traveler shares her story.

The estimate was in a letter from Gov. Gavin Newsom asking the president to deploy the naval hospital ship Mercy to increase the state's health care capacity.