Britons were forced to wait through much of Monday before the news was announced in a short statement posted on an easel set up at Buckingham Palace in London just before 9 p.m. local time (2000 GMT).

"Her Royal Highness and her child are both doing well and will remain in hospital overnight," the statement said.

Hundreds of locals and tourists alike broke into song and dance outside of the palace gates immediately after the announcement.

The baby's weight was given as 8 pounds, 6 ounces (3.75 kilograms). He had been born at St. Mary's hospital in central London some four and a half hours earlier. The duchess had entered the hospital just before 6 a.m., but this wasn't announced until more than an hour later.

Prince William issued his own a brief statement shortly after the news of the birth was made public, saying "we could not be happier."

Congratulations from abroad

Among the first foreign leaders to congratulate the royal couple was US President Barack Obama.

"We wish them all the happiness and blessings parenthood brings," President Obama and his wife Michelle said in a statement. "The child enters the world at a time of promise and opportunity for our two nations."

Congratulations were also quick in coming from some of the countries beyond Britain, of which the as yet unnamed baby can be expected to some day become head of state.

"The arrival of the newest member of the Royal family, a future Sovereign of Canada, is a highly anticipated moment for Canadians given the special and warm relationship that we share with our Royal Family," a statement issued by Canadian Prime Minister Stephen Harper said.

His Australian counterpart Kevin Rudd described the event as "a happy day for our close friends in Britain and the Commonwealth."

"We share in the joy of the Royal Family, particularly Prince Charles on the birth of his grandson, and Queen Elizabeth II on the birth of her great-grandchild," Rudd said.

Proud grandfather

Back at home, the heir to the throne described his joy at becoming a grandfather.

"It is an incredibly special moment for William and Catherine and we are so thrilled for them on the birth of their baby boy," Prince Charles said in a statement. "Grandparenthood is a unique moment in anyone's life, as countless kind people have told me in recent months, so I am enormously proud and happy to be a grandfather for the first time."

It wasn't immediately clear how long it would be before a name is made public. More celebrations were expected to be held in London on Tuesday, with artillery companies to honor the birth with gun salutes.

pfd/kms (AP, AFP, dpa)