Prince Philip is facing a fourth night in hospital as he continues to receive treatment for a bladder infection.
Philip, 91, was admitted to Aberdeen Royal Infirmary on Wednesday, during his and the Queen's annual summer break at Balmoral.
Officials said at the time that he would be in the NHS hospital for a few days, and there are no indications that he will be discharged on Saturday.
Doctors on Friday advised the Duke of Edinburgh to rest, meaning he has so far not received any visits from other members of the royal family.
At the hospital on Saturday, police can be seen guarding the main entrance.
There also remains a sizeable media presence outside the building, as there has been since news of the royal's hospital admission emerged.
However, Buckingham Palace has not issued any updates on the Duke's condition on Saturday.
He was previously said to be responding well to treatment for a recurrence of the infection he suffered in the summer.
Medics prescribed rest for the patient on Friday, but he is said to have been in constant contact with his relatives by phone.
It also emerged that an RAF search and rescue helicopter was dispatched to fly Philip to the hospital on Wednesday but poor visibility and heavy rain meant the crew were unable to reach him.
Philip made the journey of almost 80km from the castle in the Cairngorms to the city hospital by road in an ambulance instead.
His latest health scare comes less than three months after he spent five nights in hospital with a bladder infection following the Diamond Jubilee Pageant on the River Thames.
He had to miss some of the key celebrations for the Queen's 60-year reign after he was admitted to the King Edward VII Hospital in central London the day after braving wet and windy elements on a barge for several hours.
Philip also had a successful procedure to clear a blocked coronary artery in December and was in hospital for four nights over Christmas.
Prince Harry previously told how the operation had given his grandfather "a new spurt of life".
It is not yet known whether he will attend his next official engagement - accompanying the Queen to the opening of the London 2012 Paralympic Games on August 29.