The baby was born at 4:24 pm and weighs 8 pounds 6 ounces, the officials added.
The infant will be the third in line for the British throne after Prince Charles and William, who spent the long hours of labour at his wife's bedside.
Kate checked into a private wing of the St Mary's Hospital in central London early Monday morning. Soon after, a brief message on Twitter was the first of a series of carefully scripted disclosures set to culminate in the announcement of an event that has drawn unparalleled media coverage, even in the annals of Britain's headline-making royal family. "Her royal highness the Duchess of Cambridge has been admitted to St Mary's Hospital in the early stages of labour," said a message from Clarence House, the official residence of the duchess and Prince William, the duke of Cambridge.
The duchess had traveled by car to the hospital from another royal residence, Kensington Palace. Reporters outside the building said the couple had slipped into the facility through a side entrance, largely unobserved by the waiting press corps.
A spokesman for the couple, speaking in return for customary anonymity, said that the duke and duchess had traveled without a police escort. "Things are progressing as normal," the spokesman said.
There had been no official word on whether the duke and duchess were expecting a boy or a girl, and information about the birth was expected to be closely restricted.
The parents met in the early 2000s when both were students at the St Andrew's University in Scotland, and their relationship proceeded sporadically for several years until their wedding in April 2011. ' with NYT