The Queen Mother has died peacefully in her sleep at the age of 101, Buckingham Palace has announced.

"Queen Elizabeth the Queen Mother had become increasingly frail in recent weeks following a bad cough and chest infection over Christmas," said a Palace spokesman.

"Her condition detriorated this morning and her doctors were called. Queen Elizabeth died peacefully in her sleep at 3.15 this afternoon," said the spokesman.

"The Queen was at her mother's bedside," he said.