Britain's Prince William, his wife Catherine and his brother Harry urged Britons on Tuesday to talk more openly about mental health issues, saying too many people suffer in silence.

Long-standing supporters of mental health initiatives, they launched the "Heads Together" campaign in 2016, which works with charities to help tackle the stigma around mental health.

"There are times when whoever we are, it is hard to cope with challenges and when that happens, being open and honest and asking for help is life changing," William, second in line to the British throne, said in a speech.

More on this...

"For too long it has been a case of 'keep quiet and carry on'. As a result too many people have suffered in silence for too long and the effects of this can be devastating."

The three young royals were speaking at a "Heads Together" briefing in London, to promote the initiative which is "charity of the year" for the April London Marathon. For 2017, they plan to offer "Heads Together" collaborations to more organisations.

Catherine, the Duchess of Cambridge, said that not knowing how to ask for help was a particular challenge for some people.

"Admitting that they are not coping. Fear, or reticence, or a sense of not wanting to burden another, means that people suffer in silence - allowing the problem to grow larger and larger unchecked," she said.

Later on Tuesday, William and Harry attend the inaugural Endeavour Fund Awards, a project led by the three young royals' Royal Foundation that aims to help wounded servicemen and veterans with their recovery through sport and adventure.