The Queen is currently under medical supervision at Balmoral after doctors became "concerned" about her health, according to Buckingham Palace.
A statement published today by the Palace reads: "Following further evaluation this morning, The Queen’s doctors are concerned for Her Majesty’s health and have recommended she remain under medical supervision.
"The Queen remains comfortable and at Balmoral."
The monarch's immediate family have been informed with the Prince of Wales, the Duchess of Cornwall and the Duke of Cambridge are said to be travelling to Balmoral, Clarence House and Kensington Palace both confirmed.
Today Nicola Sturgeon tweeted: "All of us are feeling profoundly concerned at reports of Her Majesty’s health. My thoughts and wishes are with the Queen and all of the Royal Family at this time."
What's happening at Balmoral - follow our rolling news blog for updates on Her Majesty's health as we get them.
Prime Minister Liz Truss added: "The whole country will be deeply concerned by the news from Buckingham Palace this lunchtime" adding "my thoughts - and the thoughts of people across our United Kingdom - are with Her Majesty The Queen and her family at this time"."
The head of state pulled out of a virtual Privy Council on Wednesday after doctors ordered her to rest.
Speaker Sir Lindsay Hoyle interrupted the speech of SNP Westminster leader Ian Blackford during the energy debate to tell MPs: "I know I speak on behalf of the entire House when I say that we send our best wishes to Her Majesty the Queen and that she and the royal family are in our thoughts and prayers at this moment."
The news of her health comes a day after Boris Johnson resigned whilst Liz Truss was appointed the new PM. A Buckingham Palace spokesman said of the cancelling of the meeting: "After a full day yesterday, Her Majesty has this afternoon accepted doctors’ advice to rest.
"This means that the Privy Council meeting that had been due to take place this evening will be rearranged."
The Queen, who is 96, remains at Balmoral Castle and is not in hospital.
