Posted by 
The Queen's doctors are concerned for her health and have recommended she remain under "medical supervision", Buckingham Palace says.
In a statement released last night, the palace said the monarch remained "comfortable" at Balmoral in Scotland.
The Queen's four children, as well as grandsons Prince William and Prince Harry, headed north to be by her side.
LIVE UPDATES: Doctors concerned for Queen's health, royal family members heading to Balmoral
"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 palace said.
The announcement came a day after the 96-year-old monarch was told to rest and cancelled a meeting of her Privy Council.
The Queen's four children — Prince Charles, Princess Anne, Prince Edward and Prince Andrew — were reportedly on their way to Balmoral or already there.
Prince William, Prince Andrew, Prince Edward and Sophie, Countess of Wessex, flew into Aberdeen airport in the afternoon (overnight AEST), about an hour before driving through the gates of Balmoral Castle in a royal Range Rover.
The Duchess of Cambridge stayed in Windsor with the couple's three children.
Prince Harry, who was already in the UK, was also on his way north, a spokesperson confirmed. It was understood Meghan would stay behind for the time being.
https://twitter.com/trussliz/status/1567839967203794944
Prime Minister Liz Truss, who the Queen appointed to her position earlier in the week, said the whole country would be "deeply concerned" by the news of the Queen's health.
"My thoughts — and the thoughts of people across our United Kingdom — are with Her Majesty The Queen and her family at this time," she said, in a tweet.
Australian Governor-General Michael Hurley, the Queen's representative in the country, shared his thoughts and prayers for the monarch and the rest of the royal family.
Regular royal watchers noted the statement from Buckingham Palace went beyond the institution's customary comments regarding her "ongoing mobility issues".
Majesty magazine editor-in-chief Ingrid Seward described the statement as "unusual".
"They've been very reticent to really talk about the Queen's health in any detail," she told 9News.
"But last night in UK time the Queen was meant to be doing a Zoom meeting with her privy councillors.
"She was in Balmoral and they were in London and that was cancelled because the doctors said, you know, she wasn't well enough to do it, she was tired after meeting the prime minister at Balmoral."
Former Buckingham Palace press secretary Dickie Arbiter said it was right for people to be concerned for the monarch's health.
He said the Queen's busy Tuesday would have "taken a bit of a toll" on her majesty.
"The mobility issue is not something to be sniffed at and it would have taken all her strength to remain upright to have Boris Johnson and his resignation and then to meet with Liz Truss the incoming and new prime minister," Arbiter told the BBC.
"And then of course, as you mentioned, the cancellation of the virtual Privy Council meeting where new government ministers would be sworn in, that had to be postponed."
The royal commentator said there was "grave concern" for the monarch.
"We just need to hope that — I'm not suggesting for a moment a false alarm — but that the Queen does pull through," Arbiter said, noting that even on her most recent public appearance her majesty still had "that trademark radiant smile".
Former BBC royal correspondent Richard Sumner stressed the significance of the statement from the palace, which he said had a policy of "understatement".
"I've always suspected that possibly, along with advancing age, there may be other more complicated medical problems," he told the BBC.
"When you're 96, of course, you can't expect to have the health of a 25-year-old.
"Hopefully this is a passing storm that can be overcome. But I think judging from the careful wording of the palace, that something serious possibly is going on here.
"The fact that the Prince of Wales and the Duke of Cambridge are going up to Balmoral is a sign."
Scottish First Minister Nicola Sturgeon also shared her concern for the monarch.
"My thoughts and wishes are with the Queen and all of the royal family at this time," she said, on Twitter.
https://twitter.com/NicolaSturgeon/status/1567844387954036737
The Archbishop of Canterbury, Justin Welby, shared his prayers and those of people all across the Church of England for the Queen.
"May God's presence strengthen and comfort her majesty, her family, and those who are caring for her at Balmoral," he said.
https://twitter.com/JustinWelby/status/1567847355549978624
TIMELINE: The Queen's recent health issues
October 21, 2022: The Queen spends the night at a hospital and undergoes "preliminary investigations," according to a Buckingham palace spokesperson. She is in "good spirits" and resting at Windsor Castle.
February 20, 2022 – The monarch tests positive for coronavirus and experiences mild cold-like symptoms. UK media report that the Queen is fully vaccinated.
March 29, 2022 – She makes her first public appearance in five months when she joins the royal family and other dignitaries at a memorial service in honour of her husband Prince Philip.
June 2-5, 2022 – The Platinum Jubilee weekend celebrating the queen's 70-year reign, features a variety of public events and community activities. These including a birthday parade known as Trooping the Colour, a service at St Paul's Cathedral, a horse race, and nationwide street parties. Queen Elizabeth does not attend the church service, after experiencing "discomfort" during the opening day parade.
September 6, 2022: The Queen meets outgoing prime minister Boris Johnson and his replacement, Liz Truss, at Balmoral. It's a break from tradition, prompted by her mobility issues, for the monarch not to meet them in London.
September 7, 2022: The Queen postpones the meeting of the Privy Council after doctors advise her to rest.
Source: 9News
