Londoners and tourists expressed concern at the news that Britain's Queen Elizabeth was in hospital with gastroenteritis.
Several tourists said they had come to Buckingham Palace in the hope of seeing the 86-year-old monarch, and were disappointed that she was in hospital instead.
They wished her a speedy recovery.
Elizabeth II was hospitalised over a stomach infection that has ailed her for days, a rare instance of ill health sidelining the long-reigning monarch.
She will have to cancel a visit to Rome and other engagements as she recovers, and outside experts said she may have to be re-hydrated intravenously.
Buckingham Palace said the queen had experienced symptoms of gastroenteritis and was being examined at London's King Edward VII Hospital - the first time in a decade that Elizabeth has been hospitalised.
"As a precaution, all official engagements for this week will regrettably be either postponed or cancelled," the palace said in a statement.
Elizabeth's two-day trip to Rome had been planned to start Wednesday.
A spokeswoman said the trip may be "reinstated" at a later date.
The symptoms of gastroenteritis - vomiting and diarrhoea - usually pass after one or two days, although they can be more severe in older or otherwise vulnerable people.
Dehydration is a common complication.