A top aide to US Vice President Mike Pence has tested positive for COVID-19 one day after another White House staff member was diagnosed with the virus, BBC News reported.

Pence's press secretary Katie Miller tested positive on Friday, a day after President Donald Trump's valet.

The White House has begun daily testing for Pence and Trump, and has claimed to be taking "every single precaution to protect the president."

Six members of Pence's team were abruptly taken off his plane, Air Force 2, as he prepared to travel to Iowa to meet religious leaders.

The staff members had had recent contact with Katie Miller, according to an unnamed US official cited in the media pool report. The president and vice president had not.

Katie Miller is the wife of Trump aide Stephen Miller.

During a meeting with Republicans at the White House, Trump told reporters: "She [Katie Miller] tested very good for a long period of time and then all of a sudden today she tested positive."

When asked about the possibility of an outbreak in the White House, Donald Trump told reporters: "All you can do is take precautions and do the best you can."