People around the UK have taken part in a so-called "Clap for Carers" tribute, saluting NHS and care workers dealing with the coronavirus pandemic.
The Royal Family and the prime minister joined well-wishers who flocked to their balconies and windows to applaud.
A message from the NHS on social media described the tribute as "emotional".
The Queen said the country was "enormously thankful" to the people on the frontline of the UK's response to the virus, which causes Covid-19.
In a message on Instagram, she said the UK was grateful "for the expertise and commitment of our scientists, medical practitioners and emergency and public services".
Prime Minister Boris Johnson was joined by Chancellor Rishi Sunak outside 10 Downing Street as they took part in the national salute.
And a video posted by Kensington Palace showed Prince George, Princess Charlotte and Prince Louis clapping to thank all those healthcare staff "working tirelessly" to help those affected by Covid-19.
The Prince of Wales, the Duchess of Cornwall and their staff all separately joined in with a round of applause at Birkhall in Scotland.
Charles, who has tested positive for coronavirus, and Camilla are isolating from each other and their small number of staff.
The Clap for Carers campaign, which started online, was staged because "during these unprecedented times they need to know we are grateful", according to the organisers.
At the same time, landmarks including Belfast City Hall, Principality Stadium in Cardiff and the London Eye were lit up as part of the #lightitblue salute.
As people all over the UK went to their doorsteps and windows to take part in the round of applause, a number of celebrities shared updates about how they were paying their respects to healthcare workers.
Actress Michelle Collins shared a video taken from outside her north London home showing people taking part in the salute.
She said that the tribute had "made her cry", adding: "We love our NHS stay safe everyone emotional day."
In the video, she can be heard telling neighbours that they need "a big street party when this is all over".
TV presenter Ben Fogle shared a video of his family applauding health care workers in his living room next to a placard saying "thank you NHS".
He tweeted: "We love you NHS. We salute every one of you. Our heroes."
Star Wars actor John Boyega said it was "beautiful" hearing his neighbours "shout and clap for the NHS".
And BBC Radio 1 DJ Greg James also praised the salute on Twitter.
He wrote: "Oh my God that was properly brilliant wasn't it. Also, most brilliantly British thing ever bashing pots and pans.
"Extraordinary times can only be overcome with extraordinary acts of humanity."
The national round of applause came after the unveiling of a support package from the government to give millions of self-employed people a grant worth 80% of their average monthly profits to help them cope with the financial impact of coronavirus.
The money – up to a maximum of £2,500 a month – will be paid in a single lump sum, but will not begin to arrive until the start of June at the earliest.
Wage subsidies of 80% for salaried employees were announced last week.
It came as the government's Department for Housing advised buyers and renters to delay moving home while measures against the virus are in place.
Property listings website Zoopla predicted housing transactions will drop by up to 60% over the next three months.
Meanwhile the digital secretary has urged social media users to do their bit in tackling coronavirus-related misinformation.
Cabinet minister Oliver Dowden said the public must "remain absolutely vigilant to inaccurate stories".