The Queen is under medical supervision at Balmoral after doctors became concerned for her health, Buckingham Palace says.
“Following further evaluation this morning, the Queen’s doctors are concerned for Her Majesty’s health and have recommended she remain under medical supervision,” they said in a statement.
“The Queen remains comfortable and at Balmoral.”
Her immediate family has been informed.
The Prince of Wales and Duchess of Cornwall have travelled to Balmoral, Clarence House said. The Duke of Cambridge is also travelling there.
The announcement comes after the Queen, 96, pulled out of a virtual Privy Council on Wednesday, with doctors advising her to rest.
Prime Minister Liz Truss said the “whole country” would be “deeply concerned” by the news.
“My thoughts – and the thoughts of people across our United Kingdom – are with Her Majesty The Queen and her family at this time,” she added.
The Queen appointed Ms Truss as prime minister at Balmoral on Tuesday, instead of travelling to London for the event.