Barack Obama has congratulated the Duke and Duchess of Cambridge on the birth of their daughter.

The US President issued a message ''on behalf of the American people,'' wishing the British royals ''much joy and happiness'' following the birth of their second child this morning (02.05.15).

He said: ''Michelle and I are delighted to congratulate the Duke and Duchess of Cambridge, her Majesty the Queen and the Royal Family, and all the people of the United Kingdom on the birth of the Royal Princess.

''On behalf of the American people, we wish the Duke and Duchess and their son George much joy and happiness on the occasion of the arrival of the newest member of their family.''

The 53-year-old politician is not the first world leader to have acknowledged the birth of the princess - who is fourth in line to the throne after grandfather Prince Charles, father Prince William, and elder brother Prince George - as British Prime Minister David Cameron tweeted to celebrate the new arrival.

Posting on the social networking site, he wrote: ''Congratulations to the Duke and Duchess of Cambridge on the birth of their baby girl. I'm absolutely delighted for them.''

The arrival of the young royal was announced through the official Kensington Palace Twitter account, in which it was revealed Prince William was present for the birth.

The posts read: ''Her Royal Highness The Duchess of Cambridge was safely delivered of a daughter at 8.34am.

''The baby weighs 8lbs 3oz. The Duke of Cambridge was present for the birth.''