Prince William's wife Kate has gone into labour and been admitted to hospital for the birth of the couple's first child who will be third in line to the British throne, his office said on Monday.

After weeks of feverish media speculation over the arrival of the royal baby, Kate, 31, was taken shortly before 0500 GMT on Monday to the private wing of St Mary's Hospital in Paddington, west London, where William himself was born in 1982.

"The duchess travelled by car from Kensington Palace to the Lindo Wing at St Mary's Hospital with the Duke of Cambridge," Kensington Palace said in a statement.

"Things are progressing as normal. It wasn't an emergency."

Royal sources have said Kate has planned a natural birth with William, a Royal Air Force search and rescue helicopter pilot, to be at her side.

The sex of the baby, who will be third in line to the throne behind grandfather Prince Charles and father William, is unknown as the royal couple want it to be a surprise. Bookmakers have a girl as the firm favourite.

Newspapers have speculated Kate's sister Pippa and mother Carole Middleton might be present for the birth while Queen Elizabeth will be among the first to be informed of the arrival.

The baby will be delivered by Marcus Setchell, the queen's former gynaecologist.

Kate, who needed hospital treatment after suffering acute morning sickness in the early part of the pregnancy, made her last public appearance on June 15 at the "Trooping the Colour", a military ceremony to mark Queen Elizabeth's official birthday.

The BBC reported she entered the hospital through a back door and avoided the crowd of media from around the world who have camped outside the hospital since July 1.

The Lindo Wing, where maternity rooms cost from 5,000 pounds ($7,800) for a one-night stay, is where the late Princess Diana gave birth to William, 31, and to his younger brother Harry, who will drop a place in the line of succession after the arrival.

TRADITIONAL

The birth will be announced in the traditional way, with an envelope containing notice of the baby's details taken from the hospital to the queen's London residence, Buckingham Palace, where the news will be posted on a board outside the main gates.

"It's a lovely idea they are going to have an envelope rushed over to Buckingham Palace and the figure crossing the forecourt with the easel and putting up the announcement," royal historian Hugo Vickers told Reuters.

"I think that's absolutely great, it's rather theatrical. I think we'll all enjoy that hugely."

While the baby's sex is not known, there has been much conjecture that the child will be a girl after the duchess accepted a teddy from a well-wisher in March saying: "Thank you, I'll take this for my d...".

Whether a boy or a girl, the baby is destined to one day be monarch after Britain and other Commonwealth countries that have the queen, as their monarch agreed to change the rules of royal succession so males no longer have precedence as heir.

Royal officials have confirmed the baby will be known as His or Her Highness Prince or Princess (name) of Cambridge. Since William and Kate's wedding the April 2011 the couple has officially been known as the Duke and Duchess of Cambridge.

NAME

Bookmakers have Alexandra as the clear favourite for the baby's name, followed by Charlotte and Diana, in honour of William's mother who died in a Paris car crash in 1997. George is the favourite boy's name followed by James.

However, it might take some time for the name to emerge. The announcement of William's name took more than a week.

After the birth, commentators said Kate was expected to spend some time at her parents' house in the village of Bucklebury, about 50 miles (80 km) west of London.

The couple, who have been living in a cottage in north Wales where William is based, will eventually take up residence with their baby at Apartment 1A at London's Kensington Palace after a 1 million pound refurbishment is completed later this year. The palace was also William's childhood home.

The royal baby has already generated huge excitement globally as the couple has become global stars after some 2 billion people tuned in to watch their sumptuous marriage.

The duchess, the first "commoner" to marry a prince in close proximity to the throne in more than 350 years, is now a fashion icon, with her attire scrutinised and copied every time she steps out in public.

Analysts estimate baby fever could boost the ailing British economy by 240 million pounds ($380 million) from tourism and souvenirs. - Reuters