Prince William and his wife Catherine, Duchess of Cambridge, appear with their baby daughter outside the Lindo Wing of St Mary’s Hospital, in London on Saturday. The Duchess of Cambridge gave birth to a girl on Saturday, the couple’s second child and a sister to Prince George.

* Baby arrives after 2-1/2 hours labour

* She becomes fourth in line to the throne

* Charlotte and Alice are favourites for a name  

Reuters/London

Britain's Duchess of Cambridge, the wife of Prince William, gave birth to a girl on Saturday, the couple's second child and a sister to one-year-old Prince George.

The royal family's newest member was born at 8:34 a.m. (0734 GMT), some 2-1/2 hours after Kate Middleton was admitted in the early stages of labour to St Mary's Hospital, West London, the couple's Kensington Palace residence said in a statement.

The baby princess will be fourth in line to the throne behind her brother George, father William and grandfather Prince Charles, pushing her uncle Prince Harry down a place in the royal hierarchy.

The baby, whose name has yet to be announced, weighed 8 lbs 3 oz and William was present at the birth, the palace said.

"Her Royal Highness and her child are both doing well," it added.

Both families of the couple had been informed, including the new baby's great-grandparents Queen Elizabeth and Prince Philip. She becomes the 89-year-old queen's fifth great-grandchild.

William left the hospital later in the afternoon and soon returned with young George to introduce him to his new sister.

"I'm very happy," he told reporters and the large crowd of royal fans, some of whom have been camping outside for days.

The birth will provide a welcome distraction for many Britons from the country's knife-edge general election campaign, which comes to a head with the vote next Thursday.

Britain's leading politicians took time out from the election trail to send their best wishes.

Prime Minister David Cameron tweeted: "Congratulations to the Duke and Duchess of Cambridge on the birth of their baby girl. I'm absolutely delighted for them," while Labour leader Ed Miliband said the news was fantastic and added "I know the whole country will be wishing them well."

The birth has also provided a boon to the country's bookmakers who having first offered odds on the child's likely sex, now turn their attention to names, with Charlotte, Alice, Victoria and Elizabeth the current favourites.

Slightly longer odds are available on Diana, Eleanor and Alexandra.

William, 32, was born at the same hospital to the late Princess Diana in 1982.

He and Kate, 33, met as students at St Andrews University in Scotland, married in a spectacular ceremony at Westminster Abbey in April 2011. Their first child, George, was born in July 2013.

When Kate leaves hospital, the couple will return to Kensington Palace in central London for a couple of days before heading to Anmer Hall, their country mansion on the queen's Sandringham estate in Norfolk, eastern England.