Prince Philip, Queen Elizabeth’s 99-year-old husband, has been admitted to hospital as a precautionary measure with an ailment that is not coronavirus-related.

The Duke of Edinburgh travelled by car and walked into hospital unaided on Tuesday night after feeling unwell for a short time, a royal source said.

He is expected to remain in the hospital for a few days of observation and rest and was said to be “in good spirits”.

The palace stressed the convalescence was not an emergency but the prince, who is due to celebrate his 100th birthday on June 10, took the advice of his doctor.

“The Duke’s admission is a precautionary measure, on the advice of His Royal Highness’s doctor, after feeling unwell,” Buckingham Palace said on Wednesday.

Prince Philip is at the King Edward VII Hospital in London, where he is expected to remain for a few days of observation and rest.

He does not have a COVID-19 related illness, the royal source said.

Prince Philip, pictured with the Queen at Princess Eugenie’s wedding in 2018, rarely does public appearances anymore. Photo: Getty

The Queen, 94, remains at Windsor Castle near London, where the pair have been staying during the coronavirus lockdown with a small household staff dubbed HMS Bubble.

Both received their first dose of the COVID-19 vaccine earlier in January by a household doctor.

Within an hour of the duke’s hospital arrival, camera crews and photographers from Britain, Australia, France and Germany had gathered outside where policemen stood guard.

A spokesman for the British Prime Minister said Boris Johnson sent his ‘best wishes” as the duke “undergoes a few days of rest in hospital”.

British Health Secretary Matt Hancock said: “Really sorry to hear that His Royal Highness, the Duke of Edinburgh is in hospital.

“Sending him my best wishes for a speedy recovery.”

Media gather outside the King Edward VII Hospital in London where the Duke is staying. Photo: Getty

Philip is rarely seen in public after he stepped down from official engagements in August 2017.

He has been in and out of hospital in recent years, previously at the end of 2019 for treatment of a pre-existing medical condition.

The Greek-born former naval officer has had several stays in hospital over the last decade, including treatment for an infection in 2017 and hip replacement surgery.

-with AAP