The prince, whose official title is the Duke of Edinburgh, walked into hospital unaided on Tuesday evening after feeling unwell for a short period, a royal source said.

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

He 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.

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

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

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

The Queen, 94, remains at Windsor Castle near London, where the pair have been staying during the coronavirus pandemic.

Both received their first dose of the COVID-19 vaccine earlier in January.

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

He was previously admitted to hospital at the end of 2019.

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.

-AAP