The Lord Chamberlain, the most senior officer of the Royal Household and in charge of ceremonial events, and Sir Christopher Geidt, the Queen's private secretary, will address staff from the 91-year-old monarch's royal residences across the United Kingdom.
The revelation has sparked widespread speculation over the health of the Queen and her 96-year-old husband, Prince Philip.
However, reports indicate the meeting may not be related to health matters.
The meeting comes a day after the Queen met Prime Minister Theresa May at Buckingham Palace to formally agree the dissolution of Parliament, officially kick-starting the campaign ahead of the general election on June 8.
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Prince Philip, meanwhile, was said to be in good spirits as he unveiled a new stand at Lord's Cricket Ground yesterday.
"You're about to see the world's most experienced plaque-unveiler," he said at the event.
Later today, the Queen and Prince Philip are due at a service for members of the Order of Merit at the Chapel Royal at St James' Palace near Buckingham Palace, before hosting a lunch for those attending.
Such an emergency meeting of staff from across the country is unusual, as a meeting of royal staff is usually held as per schedule in London usually annually.
Another speculation is around a possible ceremonial announcement, like an impending royal wedding.
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