US first lady Jill Biden has tested positive for COVID-19 just days before President Joe Biden, who tested negative for the virus, is due to travel to a Group of 20 summit in India, the White House said.

Biden's 72-year-old wife, whose symptoms were described as mild, last had COVID in August of last year. The president, now 80, last tested positive in July 2022.

"This evening, the First Lady tested positive for COVID-19," her communications director, Elizabeth Alexander, said in a statement. "She will remain at their home in Rehoboth Beach, Delaware."

Biden flew back alone from Delaware on Monday evening.

"Following the First Lady’s positive test for COVID-19, President Biden was administered a COVID test this evening," the White House said. "The President tested negative. The President will test at a regular cadence this week and monitor for symptoms."

The White House did not immediately respond to a request for comment on whether Biden’s foreign travel could be affected.

But Biden's official week-ahead schedule, released shortly after the announcement of the first lady's diagnosis, showed him traveling to New Delhi on Thursday to attend the G20 summit. Biden is scheduled to fly to Hanoi on Sunday.

Biden is running for re-election in 2024 in a campaign in which the question about his age has loomed as a key issue for voters.

He is the oldest president to seek a second term, and some Republicans have said he is too old to be given another four years in the White House.

Biden's allies say he remains fit to serve as president.