Britain's royal family rushed to be with Queen Elizabeth after doctors said they were concerned about the health of the 96-year-old monarch on Thursday and said she should remain under medical supervision.

The queen, Britain's longest-reigning sovereign and the world's oldest monarch, has been suffering from what Buckingham Palace has called "episodic mobility problems" since the end of last year.

"Following further evaluation this morning, the Queen's doctors are concerned for Her Majesty's health and have recommended she remain under medical supervision," the palace said in a statement.

"The queen remains comfortable and at Balmoral."

Her eldest son and heir Prince Charles and his wife Camilla travelled to her Scottish home, Balmoral Castle, where she is staying, along with his eldest son Prince William, officials said. Her other children - Anne, Andrew and Edward - were also due to be at the castle.

A spokesperson said Prince Harry and his wife Meghan, in Britain for a number of events, would travel to Scotland.