Prince William has said his 99-year-old grandfather, Prince Philip, is "OK" after spending a sixth night in hospital.

The Duke of Cambridge was visiting a Covid-19 vaccination centre in Norfolk when he was asked about the Duke of Edinburgh's health.

At the end of his tour of the inoculation hub, set up in the King’s Lynn Corn Exchange, the duke was quizzed about Philip and replied: “Yes, he’s OK, they’re keeping an eye on him,” and gave a wink.

William spoke briefly about his grandfather after meeting people who have been vaccinated. Victoria Jones/PA WireWilliam spoke briefly about his grandfather after meeting people who have been vaccinated. Victoria Jones/PA Wire

There increasing concern concerning the duke, who is now into his seventh day at the private King Edward VII’s hospital in central London.

He was admitted on Tuesday evening as a precautionary measure after feeling unwell and walked into the building unaided.

Philip was initially due to spend a few days under medical care for “observation and rest” for the undisclosed reason, which is not coronavirus-related.

But on Friday sources told the PA news agency the duke was likely to remain in hospital into this week.

He received a visit from the Prince of Wales on Saturday – a rare occurrence as the duke is known for his “no fuss” attitude.