Queen Elizabeth has left hospital a day after she was admitted with symptoms of gastroenteritis.

A smiling and apparently fit Queen Elizabeth has left hospital a day after she was admitted with symptoms of gastroenteritis.

The 86-year-old monarch, wearing a red coat and silver brooch, shook hands with medical staff on the steps of the King Edward VII hospital before being driven away by limousine.

Buckingham Palace officials said she had first developed symptoms of the stomach bug on Friday and the decision to take her to hospital was a precautionary measure.

Royal aides suggested at the time she might stay in for a couple of days.

Gastroenteritis is an inflammation of the stomach, the intestine, or both, and it is generally caused either by food poisoning or the norovirus, a common winter vomiting bug which is very rarely dangerous.

The palace offered no further details on the Queen's condition, but confirmed that all her engagements for this week, including a trip to Italy scheduled for March 6-7, remained cancelled or postponed.

It is unusual for the monarch to cancel an engagement.

The head of state, who last year celebrated 60 years on the throne, is known for her robust health. She was last hospitalised in 2003 when she had a knee operation.

Although not as physically active as she used to be, the Queen still maintains a demanding schedule.

Unofficial court figures indicate she carried out roughly 400 official engagements in 2012 - ranging from weekly one-on-one meetings with the prime minister to gatherings of 100 or more people.

Britain's royal-obsessed tabloids all wished the monarch well, while the Daily Mail's royal correspondent, Richard Kay, wondered whether the country expected too much from her.

Kay noted that the Queen - and her 91-year-old husband, Prince Philip - spent hours on their feet in the cold and pouring rain during the river pageant meant to mark her Diamond Jubilee last year.

"Many may today be asking the same question posed after that extraordinary display of quiet physical and moral courage: Are we asking too much of the Queen?" he wrote.

But most Britons seemed to take the queen's illness in stride. There were no concerned crowds of well-wishers gathered outside the hospital - only news media keeping an eye out for royal visitors coming to pay their respects.

The Queen and the royal family have enjoyed a surge in popular support in Britain in recent years, spurred on by the wedding of her grandson Prince William to Kate Middleton in 2011.

The couple are expecting a child this summer.

The Queen's own Diamond Jubilee celebrations last year cemented her popularity, as did her participation in the opening ceremony of the London Olympic Games, appearing alongside the fictional spy James Bond in a video sequence hailed as one of the highlights of the show.

- Reuters and AP