Britain's Prime Minister Rishi Sunak read from the biblical book of Colossians at the coronation of King Charles III in keeping with the tradition of British Prime Ministers giving readings at state occasions.

Mr Sunak, Britain's first Prime Minister of Indian heritage and a practising Hindu, reading from a biblical book will resonate with the multi-faith theme being struck for the Christian ceremony.

Mr Sunak described the coronation as "a proud expression of our history, culture and traditions".

The service has been designed to reflect the changes in the UK since King Charles' mother Queen Elizabeth II's coronation in 1953, the character of Britain as it is today, and the Church of England's role in contemporary society.

As one of the newer elements, the 74-year-old monarch also prayed aloud using words specially written for the occasion that reflect the "duty and privilege of the Sovereign to serve all communities".

Thousands have congregated at the Abbey today and millions are watching the live telecast on screens.

But even before King Charles and Queen Camilla, 75, left Buckingham Palace aboard the Diamond Jubilee State Coach for a rainy procession to the Abbey, police arrested dozens of protesters using new powers rushed onto the statute book to crack down on direct action groups, news agency AFP reported.

The coronation is the first since 1953 and the first of a king since 1937. It is only the second to be televised and the first in colour and streamed online.

Much of the two-hour Anglican service, led by the Archbishop of Canterbury Justin Welby, would be recognisable to the 39 other monarchs crowned at Westminster Abbey since 1066.