Britain's new Prime Minister Liz Truss paid emotional tribute in parliament Friday to the late queen and pledged the nation's "loyalty and devotion" to King Charles III.

Elizabeth II was "one of the greatest leaders the world has ever known", Truss told a hushed House of Commons, calling her "the nation's greatest diplomat".

"Her legacy will endure through the countless people she met, the global history she witnessed and the lives that she touched," Truss added, before addressing the "awesome responsibility" now borne by Charles.

"Even as he mourns, his sense of duty and service is clear," she said, at the start of two days of special tributes in parliament following the queen's death on Thursday.

"He has already made a profound contribution through his work on conservation, education and his tireless diplomacy. We owe him our loyalty and devotion."

Truss said Charles would lead Britain "to a new era of hope and progress".

"The Crown endures. Our nation endures. And in that spirit, I say God save the king."