Here's what we know so far about the emergency meeting at Buckingham Palace.

The entirety of Queen Elizabeth II’s staff has been summoned from across the United Kingdom to Buckingham Palace for an emergency meeting scheduled for Thursday morning.

It is understood the meeting was called suddenly on Wednesday evening.

It is reported staff will be addressed by Lord Chamberlain – the Royal Household’s most senior officer – and the Queen’s private secretary, Sir Christopher Geidt within a number of hours.

The calling of the meeting has been described as unusual and has begun a wave of rumours about the health and wellbeing of the Queen, who recently turned 91, and the Duke of Edinburgh, who is approaching his 96th birthday.

"Everyone is on tenterhooks," one palace aide told the Daily Mail. 

"Although meetings involving the entire royal household are occasionally called, the way this has been done at the eleventh hour is highly unusual and suggests that there is something major to be disseminated," the source continued, adding, "at the moment, only those closest to her genuinely know what on earth this is all about."

In recent years, both her Majesty and the Duke have reduced the number of commitments they undertake but even in their 90s, the couple remains unusually active, attending up to 300 events per year each.

On Wednesday, her Majesty was seen meeting with British Prime Minister Teresa May and the Duke attending an event at Lords Cricket Ground.

According to The Guardian, when the Queen dies, a newsflash announcement will be released to global media outlets, and at the same time, a footman dressed in mourning clothes will exit Buckingham Palace to pin a black-edged written notice to the palace gates.

Royal experts also say the official palace website will be updated to show a single-colour background and the same message posted to the gates.

More information is expected at 5pm EST.