Kate Middleton, the Duchess of Cambridge, on Sunday launched a book of photographic portraits taken during Britain's COVID-19 lockdowns that she said would provide a lasting record of the pandemic.

Kate Middleton, who is married to Prince William, the Queen's grandson and second in line to the throne, began the project with the National Portrait Gallery last year, inviting people to submit photos taken during Britain's first coronavirus lockdown.

A panel of judges including Kate chose 100 portraits from over 31,000 entries, which were shown in digital and community exhibitions before the book was announced.

"Through 'Hold Still', I wanted to use the power of photography to create a lasting record of what we were all experiencing - to capture individuals' stories and document significant moments for families and communities as we lived through the pandemic," Kate wrote in the introduction to the book.

The book, called "Hold Still: A Portrait of Our Nation in 2020", will be available from May 7, exactly a year after the project began.

Net proceeds will be split between the National Portrait Gallery and the British mental health charity Mind.