President Donald Trump has broken his social media silence since it emerged he would be taken to hospital for coronavirus treatment.
The US president tweeted on Saturday morning: "Going well, I think! Thank you to all. LOVE!!!"
The leader and First Lady Melania Trump confirmed they had tested positive for Covid-19 yesterday.
Later in the day it was announced Trump, 74, would be flown to hospital for "a few days" on the advice of his doctors.
An adviser speaking to CNN said the President had been having trouble breathing and had been very fatigued.
He has been suffering "mild symptoms", including cold-like symptoms, fatigue and a mild fever, according to officials.
He had walked to and from his helicopter flight from the White House to the hospital, giving a thumbs up as he boarded the Marine One.
But according to reports, the US president's condition seemed to be "serious" as he spent his first night in hospital after testing positive for coronavirus.
CNN reported an official saying there is "reason for concern" about his health and that the situation was "serious".
But the aide assured the public should not be alarmed and has said the American leader is taking the situation "very seriously".
Trump is being treated with Remdesivir at Walter Reed Medical Center, an intravenous antiviral drug that has been shown to shorten hospital stays.
Trump had been flown to the hospital by helicopter for treatment on Friday evening, where officials said he would continue working from a special suite there as he is treated.
He has not transferred power to Vice President Mike Pence.
Trump's illness came just days after the opening round of his battle to hold onto the US presidency.
He clashed with rival Joe Biden in a fiery presidential debate.
A series of Trump officials have confirmed they have also tested positive for the virus, including his campaign manager.
Biden himself tested negative for the virus, following the debate with Trump.
In a video statement published on his Twitter account shortly after his departure for hospital, Trump said: "I want to thank everyone for their tremendous support. I'm going to Walter Reed hospital.
"I think I'm doing very well, but we're going to make sure things work out. The First Lady is doing very well.
"So thank you very much. I appreciate it. I will never forget it. Thank you."
Mr Trump, 74, is considered to be at greater risk of serious harm from the virus because of his age and weight.
