US President Donald Trump had a high fever and his blood oxygen level "dropped rapidly" before he went to hospital, according to his top aide.
Speaking to Fox News today, Trump chief of staff Mark Meadows said the President was increasingly worried about his health following his Covid-19 diagnosis.
"Yesterday morning, he was real concerned with that. He had a fever and his blood oxygen level had dropped rapidly," he told host Jeannie Pirro.
He added that the President had shown "unbelievable courage," was doing "extremely well" and he was "very optimistic" for his recovery.
Trump's main doctor said the medical team treating the commander in chief is "cautiously optimistic," but also noted, as Meadows did, he is "not yet out of the woods".
The latest assessment came today from Navy Commander Dr Sean Conley. He reported Trump had been up and around at his medical suite at Walter Reed National Military Medical Center during the day and had been conducting business.
Medical experts say the disease caused by Covid-19 can become more dangerous as the body responds to the infection over time.
Trump is expected to remain at Walter Reed for several more days.
A slightly hoarse and pale Trump earlier issued a four-minute video on Twitter, saying he "wasn't feeling so well" when he was admitted to hospital - but was starting to feel better.
"I came here, wasn't feeling so well, I feel much better now we're working hard to get me all the way back, I have to be back because we still have to make America great again," he said.
He said he was starting to "feel good" but said he did not know what would happen over the next few days: "I guess that's the real test."
In the video he said he thought he would be back soon on the election trail: "I look forward to finishing up the campaign."
He said he was fighting for the millions of people who have also contracted the virus "all over the world".
"We are going to beat this coronavirus or whatever you want to call it."
Trump said he chose to be taken to the hospital despite having the option to stay at the White House. But he said he couldn't do that due to the strict social distancing and quarantine measures that he would be under.
"This is America, this is the United States, this is the greatest country in the world, this is the most powerful country in the world, I can't be locked up in a room upstairs."
EARLIER
President Donald Trump went through a "very concerning" period and the next 48 hours will be critical in terms of his care as he battles the coronavirus at a military hospital, White House chief of staff Mark Meadows said.
The comments came after it was revealed that Trump was administered supplemental oxygen Friday morning at the White House before he was transported to the hospital, although staff insisted he had only mild symptoms.
Trump's doctors, for their part, painted a rosy picture of the president's health in a press conference at Walter Reed National Military Medical Center. But the briefing by Navy Commander Dr. Sean Conley and other doctors raised more questions than it answered.
Conley left murky the issue of whether the president needed supplemental oxygen and declined to discuss exactly when he fell ill. Conley also revealed that Trump began exhibiting "clinical indications" of Covid-19 on Thursday afternoon, earlier than previously known.
According to the person familiar with Trump's condition, Trump was administered oxygen at the White House before he was transported to the military hospital. The person, who was not authorised to speak publicly and spoke to The Associated Press on condition of anonymity.
Conley, updating the nation on the president's condition from Walter Reed, said Trump had been fever-free for 24 hours.
Trump was admitted to the hospital on Friday after testing positive for the coronavirus and has been undergoing treatment.
While Conley said the president was not currently on oxygen, he refused to say whether the president had ever been on oxygen, despite repeated questioning.
"Thursday no oxygen. None at this moment. And yesterday with the team, while we were all here, he was not on oxygen," he said.
Doctors said Trump was doing well and his symptoms were subsiding.
Just had another great call with @POTUS. He sounds well and says he’s feeling good. We talked about the people’s business — fighting the pandemic, confirming Judge Barrett, and strengthening the economy for American families. Let’s keep our President & First Lady in our prayers.
The WH TV pool just received this quote from “a source familiar with the President's health...” - “The President's vitals over last 24 hours were very concerning and the next 48 hours will be critical in terms of his care. We are still not on a clear path to a full recovery."
Conley said 72 hours into his diagnosis, Trump's mild cough, nasal congestion and exhaustion were now "resolving and improving".
Days 7-10 were the critical period in a Covid infection, said Conley, who spoke alongside nine other medical staff at the hospital.
He said Trump and his wife Melania were "extremely grateful for prayers" from people.
"I feel like I could walk out of here today," another physician, Sean Dooley, reported Trump as saying, as he was being cared for at the medical center.
Doctors, Nurses and ALL at the GREAT Walter Reed Medical Center, and others from likewise incredible institutions who have joined them, are AMAZING!!!Tremendous progress has been made over the last 6 months in fighting this PLAGUE. With their help, I am feeling well!
Today he would be encouraged to be up and about, and completing his usual work, said Dooley. "He's in exceptionally good spirits," said Dooley.
He would not answer questions about how the President came to be infected.
He said in terms of risk factors, the President was a little bit overweight but his blood pressure and heart rate were normal. "I've had no concerns there."
First Lady Melania Trump - who has also tested positive - was "doing great", showing no symptoms, and did not require hospitalisation.
The administration has consistently been less than transparent about the president's health as the virus spread inside the White House.
Aides had declined to share basic health information about the president, including a full accounting of his symptoms, what tests he's undertaken and the results. The first word that a close aide to Trump had been infected came from the media, not the White House.
In a memo released shortly before midnight, Conley did report that Trump had been treated at the hospital with remdesivir, an antiviral medication, after taking another experimental drug at the White House. He added that Trump is "doing very well" and is "not requiring any supplemental oxygen."
The White House said Trump was expected to stay at the hospital for "a few days" out of an abundance of caution and that he would continue to work from the hospital's presidential suite, which is equipped to allow him to keep up his official duties. In addition to accessibility to tests and equipment, the decision was made, at least in part, with the understanding that moving him later, if he took a turn for the worse, could send a worrying signal.