Queen Elizabeth II's 99-year-old husband Prince Philip will spend more time in a London hospital where he is being treated for an unspecified condition, Buckingham Palace said on Tuesday.

"The Duke of Edinburgh remains at King Edward VII's Hospital where he is receiving medical attention for an infection," a statement said.

"He is comfortable and responding to treatment but is not expected to leave hospital for several days."

Philip, who has been married to the queen for 73 years, was admitted to the private London hospital a week ago as a "precautionary measure" after he felt unwell, according to the palace.

His youngest son, Prince Edward, earlier told Sky News television that his father was "a lot better..., and he's looking forward to getting out.

"So we keep our fingers crossed."

Edward said his father was feeling frustrated inside the hospital as "you can only watch the clock so many times and the walls are only so interesting.

"We've had some brilliant and lovely messages from all sorts of people and we really appreciate that and so does he, I've been passing them on," he added.

On Monday, Philip's grandson, Prince William, said the duke was "OK" and being closely monitored by medical staff.

The prince was able to walk into the hospital unaided last Tuesday after arriving in private transport rather than an ambulance, a source said at the time.

Palace sources have said that his admission was not coronavirus-related. Both he and the Queen received first doses of a Covid-19 vaccine in January.

Heir to the throne Prince Charles visited his father in hospital on Saturday but did not comment on his state of health.

Philip, a former naval officer, was treated at the same hospital in August 2012 after a recurrence of a bladder infection that laid him low during the queen's diamond jubilee celebrations.

The previous year, he had a stent fitted after suffering a blocked coronary artery.