Alarm mounted further after at least two Republican lawmakers who recently met with President Donald Trump announced they were going into self-quarantine, fearing that they were exposed to the virus at a conservative conference just outside Washington, AFP reported.

Trump has not been tested for the virus, White House press secretary Stephanie Grisham said.

"He has neither had prolonged close contact with any known confirmed COVID-19 patients, nor does he have any symptoms," she said in a statement.

Asked if Trump had been tested for the virus, Vice President Mike Pence said: "I honestly don't know."