Prince Philip will spend “several” more days in a hospital where he is being treated for an infection, Buckingham Palace has revealed.

The announcement comes a week after Philip, who turns 100 on June 10, was admitted to King Edward VII’s hospital in central London after becoming unwell at Windsor Castle.

The palace previously stressed the convalescence was not an emergency and the Duke’s illness is not related to COVID-19.

“He is comfortable and responding to treatment, but is not expected to leave hospital for several days,” Buckingham Palace said on Wednesday morning (Australian time).

His youngest son Edward said his 99-year-old father was getting a lot better.

“As far as I’m aware, he’s a lot better … so he’s looking forward to getting out ,which is the most positive thing,” he told Britain’s Sky News.

Edward said that his father was “just a bit” frustrated at being in hospital.

“You can only watch the clock so many times and the walls are only so interesting,” he added.

“We’ve had some lovely messages from all sorts of people and we really appreciate that and so does he, I’ve been passing them on.”

Both Philip and the 94-year-old Queen, who has stayed at Windsor Castle, her home to the west of London, have received their first dose of the coronavirus vaccine.

The upbeat assessment echoes that of Prince William, son of heir Prince Charles, who said on Monday his grandfather was “OK, they’re keeping an eye on him”.

Philip has required hospital treatment a number of times in the last decade for a recurrence of a bladder infection and he had an operation to clear a blocked artery in his heart after suffering chest pains.

-with AAP