The Duchess of Cambridge has entered the early stages of labour, Kensington Palace has confirmed
The Duchess was admitted to St Mary's Hospital in the early hours of the morning in the UK, or around 3pm (AEST).
"The Duchess of Cambridge has been admitted this morning to St. Mary’s Hospital, Paddington, London in the early stages of labour," a royal spokesman said.
She was rushed to the west London hospital by car around 6am local time and was accompanied by her husband Prince William.
The Duchess was admitted to a the hospital's private Lindo Wing as the media pack that has been hovering around the royal couple for weeks entered a frenzy.
Middleton was due to give birth in mid-July so the baby appears to have come around a week late.
Kate is being tended by a top medical team led by the Queen's former gynaecologist Marcus Setchell, who delivered the Countess of Wessex's two children.
Assisting him is Alan Farthing, the former fiance of murdered TV presenter Jill Dando and the Queen's current gynaecologist.
The world's press have been camped outside St Mary's in Paddington for days in anticipation of the birth.
The hospital's Lindo wing is a private obstetric unit, with prices starting at just under 5000 pounds ($8,284) for a normal delivery package over 24 hours, with consultants' fees around 6000 pounds ($9,944) extra depending on the care required.
Prices increase if the delivery is a difficult one or the mother has a caesarean section.
But Kate is intending to have a natural birth and does not know whether she is going to have a boy or girl.
The news that what had been dubbed by bored journalists 'the Great Kate Wait' was finally over was announced in a brief statement from Kensington Palace at 7.30am after rumours she had been spotted began circulating.
The child will become third in-line to inherit the throne currently occupied by its great grandmother Queen Elizabeth II.
After a recent change in the law, the baby will also be made an HRH (His or Her Royal Highness) and given the title Prince or Princess of Cambridge.
The baby does not necessarily need to have a surname — but if William and Kate want it to have one, they can choose between Mountbatten-Windsor, Wales and Cambridge.
The last time a serving monarch had the chance to meet a great grandchild born in direct succession to the crown was almost 120 years ago.
The Duke and his younger brother Prince Harry were born in the Lindo wing and the Prince and Princess of Wales famously posed on the building's steps in 1982 holding baby William in turn.
Betting on the name of the royal baby, which will be third-in-line to the throne, has produced one favourite with a number of bookies - Alexandra.
Many punters believe William and Kate will have a girl and have put their money on the name.
Other monikers that have attracted royal fans include Charlotte, Diana, Elizabeth and Victoria, with George and James picked by those who think the new baby will be a boy.
William will take paternity leave from his job as an RAF search and rescue helicopter pilot.
But it is not known how long the Duchess will take off from her royal duties to care for her first child.
The new royal baby will be the Queen's third great-grandchild and is destined to be crowned monarch.
It will be the 43rd sovereign since William the Conqueror if, as expected, it follows reigns by Charles then William.
The Duke is known to want a daughter while the Duchess is hoping for a son.
Recent changes to the rules of succession mean if a girl is born she will not be leapfrogged by a younger brother at a later date.
The sex of an infant in direct line to the throne no longer determines whether he or she wears the crown.
Author: Martin Zavan, Approving editor: Matthew Henry