WASHINGTON (REUTERS, BLOOMBERG) - US President Donald Trump's national security adviser, Mr Robert O'Brien, has tested positive for the novel coronavirus, but there is no risk of exposure to Mr Trump or Vice-President Mike Pence, the White House said in a statement.

"He has mild symptoms and has been self-isolating and working from a secure location off site. There is no risk of exposure to the President or the Vice-President. The work of the National Security Council continues uninterrupted," according to the statement.

The White House has said staff is regularly tested for the virus, and Mr O'Brien is the most senior official to be found positive amid the pandemic.

A US military member who works at the White House as a valet tested positive for coronavirus in May as did Vice-President Pence's press secretary.

Mr O'Brien, 54, has been out of the office since late last week, according to a person familiar with the matter. He contracted the virus while taking a few days off from work, spending time with his family.

Since his diagnosis, Mr O'Brien has been isolating at home while still running the National Security Council, doing most of his work by phone, another person said. The people asked not to be named to discuss details that aren't yet public.

Mr O'Brien and senior staff on the NSC are tested daily for Covid-19. His office is near the Oval Office and Mr Pence's West Wing office.

Mr O'Brien's infection comes as the pandemic continues to surge with infections and deaths on the rise in many US states.

Mr Trump last week resumed regular briefings to reporters about the virus after polls showed voters increasingly disapprove of the president's handling of the virus.

There have been 16.2 million cases of coronavirus since the pandemic began earlier this year, with deaths passing 648,000, according to data collected by Johns Hopkins University. In the US, there have been more than 4.2 million cases and 146,935 deaths, according to the data.

The president has changed his message in recent days on the virus.

Last week, Mr Trump abruptly called off Republican National Convention activities set for August in Jacksonville, Florida, citing concerns over the virus. He began promoting use of masks after downplaying the need for them.

Mr Trump also said some public schools may not be able to open on time in virus hot spots, after earlier calling on them to restart.

NSC staff were not informed that Mr O'Brien had tested positive, one person familiar with the matter said. Some found out through press reports, they said.