Britain's Prince Philip, the husband of Queen Elizabeth II, was spending a second night in a London hospital, with sources saying it was not due to coronavirus symptoms.

File photo of Britain's Prince Philip. (Photo: AFP)

The 99-year-old was said to be "in good spirits" in the private King Edward VII Hospital in Marylebone, where the palace said he was taken on Tuesday evening after feeling unwell.

The Duke of Edinburgh, as he is formally known, "is expected to remain in hospital for a few days of observation and rest", the palace statement added.

Sources told AFP he was not taken in by ambulance and had felt well enough to walk into the hospital.

Police officers stood outside the hospital in central London.

Police officers and doormen stand at the entrance to King Edward VII hospital in central London on February 17, 2021 where Britain's Prince Philip, Duke of Edinburgh was admitted. (Photo: AFP)

The 99-year-old was said to be "in good spirits" in the private King Edward VII Hospital in Marylebone, where the palace said he was taken on Tuesday evening after feeling unwell.

The Duke of Edinburgh, as he is formally known, "is expected to remain in hospital for a few days of observation and rest", a statement from Buckingham palace said Wednesday.

Sources told AFP he was not taken in by ambulance and had felt well enough to walk into the hospital.

Police officers stood outside the hospital in central London.

Prime Minister Boris Johnson's office said he had sent his "best wishes to the Duke of Edinburgh as he undergoes a few days of rest in hospital".

The royal family continued their duties on Wednesday, with the Queen speaking to the Royal Navy Admiral Tony Radakin from Windsor Palace, while Prince Charles and the Duchess of Cornwall visited a hospital in Birmingham.