President Xi Jinping extended on Saturday his wishes for a speedy recovery to his US counterpart, Donald Trump, and First Lady Melania Trump, following their coronavirus diagnoses.

US President Donald Trump was in a military hospital on Saturday for treatment. He went through a "very concerning" period on Friday, and the next 48 hours "will be critical" for his care, White House chief of staff Mark Meadows said on Saturday

In a message to Trump, Xi said that on learning Trump and Melania had tested positive for COVID-19, he and his wife, Peng Liyuan, extended their sympathies and wished them a speedy recovery.

Trump was in a military hospital on Saturday for treatment. He went through a "very concerning" period on Friday, and the next 48 hours "will be critical" for his care, White House chief of staff Mark Meadows said on Saturday.

In a four-minute video clip posted on Twitter on Saturday evening, Trump said he was feeling "much better" and that he thinks he will "be back soon".

"I came here. Wasn't feeling so well. I feel much better now, we're working hard to get me all the way back," said the president, who was sitting behind a desk wearing a blue jacket and a white shirt with the collar button undone.

Trump will work in a special suite at the hospital for the next few days as a precautionary measure, White House press secretary Kayleigh McEnany said.

Early on Friday, he tweeted that he and the first lady had contracted the virus.

Trump, 74, has a mild fever, according to a source familiar with the matter. White House doctor Sean P Conley said late on Friday that Trump was doing very well, and did not need supplemental oxygen.

The coronavirus pandemic has killed more than 200,000 people in the United States and hammered the country's economy.

READ MORE: US digesting coronavirus death toll of 200,000

A number of other prominent Republicans also tested positive on Friday, including former White House senior adviser Kellyanne Conway and Republican senators Mike Lee and Thom Tillis.

On Saturday, Republican Ron Johnson, chairman of the Senate Homeland Security Committee, was diagnosed with COVID-19.

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US Vice-President Mike Pence, who would take over presidential duties if Trump became severely ill, tested negative, a spokesman said. The former Indiana governor, 61, is working from his own residence about 5 kilometers from the White House.

Xinhua, agencies and Cui Haipei in Beijing contributed to this story.