Queen Elizabeth II has been placed under medical supervision after Doctors expressed concerns over her health.
“Following further evaluation this morning, the Queen’s doctors are concerned for Her Majesty’s health and have recommended she remain under medical supervision,” a statement said.
The Queen is comfortable, it added.
It is very unusual for Buckingham Palace to put out a statement like this – it is usually unwilling to provide a commentary on the 96-year-old monarch’s medical matters, which are seen as private.
Prince Charles has travelled to Balmoral with his wife, the Duchess of Cornwall.
The Duke of York and the Count and Countess of Wessex are travelling to the Scottish estate, about 40 miles (64km) west of Aberdeen.
Princess Royal, Princess Anne, was already in Scotland undertaking engagements.
The Duke of Cambridge is also on his way, with the Duchess of Cambridge remaining in Windsor with their children on their first full day at school.
The Duke and Duchess of Sussex, who were due to attend a charity event in London, are travelling to Balmoral, their spokesperson said.
Barriers are being placed outside one of the entrances to the estate.
Reacting to the news, UK 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, instead of travelling to London for the event.
During her 70-year reign, the Queen has typically had an audience with her new prime minister at Buckingham Palace.
The Archbishop of Canterbury, Justin Welby, said: “My prayers, and the prayers of people across the [Church of England] and the nation, are with Her Majesty The Queen today.
“May God’s presence strengthen and comfort Her Majesty, her family, and those who are caring for her at Balmoral.”
