LONDON (AFP) - The Duchess of Cambridge has given birth to a girl, hours after going into labour, Kensington Palace announced on Saturday.

"Her Royal Highness The Duchess of Cambridge was safely delivered of a daughter at 8.34am," the royal couple's residence said in a tweet.

"The baby weighs 8lbs 3oz. The Duke of Cambridge was present for the birth," it added.

Mother and baby "are both doing well," it said.

The child, who will be known as Her Royal Highness Princess of Cambridge, is the second child for the Duchess, Kate, and her husband, Prince William.

Prince William was present for the birth and all senior members of the royal family have been told the news, which was first announced in a tweet and then by the traditional colourfully-dressed town crier on the steps of the St Mary's hospital in London.

A proclamation signed by the royal doctors was also placed on a gilded easel in front of Buckingham Palace, where hundreds of curious onlookers crowded in front of the gates to witness the historic moment.

The new princess, who weighed in at 8 pounds 3 ounces (3.7 kilos), comes after big brother George in the line of succession, below Queen Elizabeth II's eldest son Prince Charles and his eldest son William.

The names favoured by bookmakers are Alice and Charlotte.

Media teams from around the world had rushed to the private maternity wing of St Mary's hospital in the early morning, joining a group of royal superfans who have remained camped outside for more than a week.

There were cheers in the crowd after the birth, with supporters singing: "It's a girl! It's a girl!" "I'm so pleased,"

Margaret Tyler, 71, who wore a jacket in the colours of the British Union Jack flag and a badge in honour of William's late mother Diana. "William wanted a girl and Diana wanted a girl. I think it's just nice for George to have a little sister," she said.

Another royal supporter, John Loughrey, said: "I'm so happy. I can't tell you. It's a lovely feeling. I'm feeling very happy for the royal family."

Royal fan Kathy Martin donned a pink party hat and started dancing on the spot. "It's the happiest news, just what we've been waiting for," she said.

'Unforgettable day'

At Buckingham Palace, a queue formed to file past the easel announcing the royal birth.

"It's an unforgettable day in my life," said Joy Buttinger, a nurse living in Austria who was on holiday with her 18-year-old daughter.

Kensington Palace said Kate was admitted to the hospital accompanied by her husband at around 6.00 am in the early stages of labour.

British Prime Minister David Cameron sent his best wishes in a tweet. "The whole country will wish her well," he wrote shortly after she was admitted.

Within minutes of the news that Kate had gone into labour, the news was trending on Twitter with the hashtag #royalbaby and more and more curious onlookers could be seen arriving at the private clinic in the city centre.

Guy Thorpe-Beeston, surgeon-gynaecologist to the royal household and a specialist in high-risk pregnancies, led the delivery team.

Kensington Palace had announced Kate's pregnancy in September and she struggled with severe morning sickness as she did in her first pregnancy. William has told supporters the second child will be a "game-changer" after the first "life-changer".

William and Kate are planning to spend the first few days after the birth at Kensington Palace. They will then travel to Anmer Hall, a secluded 10-bedroom country mansion on Queen Elizabeth's privately-owned Sandringham estate in Norfolk, eastern England, where they have set up home.

The baby's name may not be revealed for several days. William's name was not announced for a week, while the world had to wait one month after Charles was born. George was named two days after his birth.

The princess will be christened as a member of the Church of England, wearing a replica of the intricate lace and satin gown made for queen Victoria's eldest daughter in 1841. Experts say the royal birth could inject tens of millions of pounds into the British economy, with a baby princess particularly lucrative because she could become a fashion trendsetter.