All the Queen's children are gathering at, or are travelling to, her Scottish estate near Aberdeen.

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

The Queen is "comfortable", it added.

It is very unusual for Buckingham Palace to put out a statement like this - it is usually unwilling to provide a commentary on the 96-year-old monarch's medical matters, which are seen as private.

Her son, Prince Charles, is at Balmoral with his wife, Camilla, the Duchess of Cornwall.

Her grandson, the Duke of Cambridge, other sons, the Duke of York and the Earl of Wessex, and his wife Sophie, the Countess of Wessex, arrived at Aberdeen airport just before 16:00 BST.

They are travelling to the Queen's Scottish estate, about 40 miles (64km) west of Aberdeen.

BBC News/Sean Coughlan, royal correspondent, & George Bowden