US President Donald Trump said he and first lady Melania Trump underwent a Covid-19 test after a top aide he spent substantial time with this week tested positive for the disease.

Trump took to his Twitter account and said that they are awaiting the test results and are beginning a quarantine process.  His Tweet came after Hope Hicks, one his aides, had tested positive for the virus.

U.S. President Donald Trump and first lady Melania Trump take part in the 17th annual September 11 observance at the Flight 93 National Memorial near Shanksville in Stoystown, Pennsylvania.REUTERS

She had travelled with the President on Air Force One earlier this week, the source added. In a Fox News interview late Thursday night, Trump appeared unsure about what his top aide's positive test meant for him.

Whether we quarantine or whether we have it, I don't know

"I just went out with a test and the First Lady just went out with a test also," he said. "So whether we quarantine or whether we have it, I don't know."

Taking to Twitter after the interview, the President said: "Hope Hicks, who has been working so hard without even taking a small break, has just tested positive for Covid 19. Terrible. The First Lady and I are waiting for our test results. In the meantime, we will begin our quarantine process."

Also in a statement, a White House official said contact tracing has been done, "and the appropriate notifications and recommendations have been made", The Hill news website reported It was not immediately clear if Trump planned to self-quarantine out of an abundance of caution. He has events scheduled for Friday in Florida and Saturday in Wisconsin.

Hicks is the latest White House aide to test positive for the virus which has so far infected 7,277,352 people in the US and killed 207,791 others, making it the worst-hit country in the world. National Security Adviser Robert O'Brien had tested positive, as well as a White House valet who serves the President.

Katie Miller, the Vice President's communications director and the wife of Trump senior adviser Stephen Miller, were also infected.