The Queen will speak to the nation on Sunday about the coronavirus outbreak – only her fourth special address at a time of crisis during her 68-year reign.
Buckingham Palace said the message, recorded at Windsor Castle, will be broadcast on TV and radio at 20:00 BST.
The Queen records annual Christmas messages but other addresses are rare.
It comes as the number of people who died with coronavirus in the UK rose by 684 in 24 hours, latest figures show.
The Department of Health said that as of 17:00 BST on 2 April, the total number of deaths is now 3,605, up from 2,921. There are 38,168 confirmed cases.
In Scotland, the number of deaths has risen by 46, while in Wales a further 24 people died. In NI, the number of people who died with coronavirus has risen by 12.
The Queen’s address will be broadcast on TV, radio and social media, Buckingham Palace said.
There have only been three occasions when the Queen has broadcast speeches in troubled times: after the Queen Mother’s death in 2002; ahead of Diana, Princess of Wales’s funeral in 1997; and during the First Gulf War in 1991.
The Queen also made a televised address to mark her Diamond Jubilee in 2012.
The monarch, 93, released a statement about the outbreak last month, when the number of UK deaths stood at 144.
She said the UK was “entering a period of great concern and uncertainty” and praised the work of scientists, medics and emergency staff, saying everyone has a “vitally important part to play”.
BBC royal correspondent Nicholas Witchell said Sunday’s speech had been decided “in close consultation with Downing Street” as “they have had it in their minds for some days now”.
“It is clearly a measure of the seriousness of the situation in which this country and indeed the wider world finds itself,” he said.
He suggested the speech might include thanks for NHS staff and key workers, as well as an emphasis on the important role individuals can play – while also aiming to reassure and rally people.
The heir to the throne, Prince Charles, was seen in public for the first time on Friday after being diagnosed with coronavirus and spending seven days in self-isolation.
He opened the first of the National Health Service’s emergency field hospitals to treat coronavirus patients in east London’s ExCel centre.
The exhibition space – usually used for large events such as Crufts and Comic Con – was transformed into a hospital in just nine days.
The temporary NHS Nightingale Hospital is able to care for as many as 4,000 patients and is the first of several such facilities planned across the UK, including Glasgow, Belfast, Cardiff, Manchester and Birmingham.
Meanwhile, Prime Minister Boris Johnson, who announced he had contracted the virus last Friday, says he will carry on self-isolating after continuing to display mild symptoms of the virus including a high temperature.