If Johnson is unable to carry out his official duties, his role would likely be filled temporarily by Dominic Raab, the U.K.'s foreign secretary and first secretary of state.
At midnight Thursday, security forces began enforcing the order against all but essential movement. Meanwhile, the health ministry reported two COVID-19 deaths among nearly 1,000 confirmed cases.
The leaders spoke after a virtual G-20 meeting. President Trump called it a "very good conversation," and China state TV said Xi Jinping offered to help the U.S. respond to the spread of the virus.
Boris Johnson announced on Twitter that he's developed mild symptoms of the Coronavirus, and took the test on the advice of the chief medical officer. Johnson is working from home.
The U.S. last week closed its borders with Canada and Mexico because of the coronavirus outbreak. At the southern border, the closure is affecting life on both the U.S. and Mexico sides.
They have seen patients who presented with these symptoms — then tested positive for the novel coronavirus. Now they're gathering data to see if they can prove that there is indeed a connection.
As a virus makes copies of itself, errors may creep in, changing its genetic makeup. Researchers are trying to determine if the changes are significant in the new coronavirus.
The torch relay was supposed to start on Thursday in the Japanese prefecture hit hard by the 2011 earthquake and tsunami. A torch runner recalls the disaster that took his family.