Britain's Princess Charlotte was christened in an intimate ceremony on Sunday, in the royal baby's second public appearance since her birth nine weeks ago to proud parents Prince William and Kate.

Just 21 guests attended the low-key baptism held inside the 16th century Church of St Mary Magdalene on the country estate of the baby's great-grandmother Queen Elizabeth II, as crowds waited outside.

Overnight campers and early risers, many wearing Union Jack-printed clothing, had braved wet weather to get a prime spot on the paddock outside the church at Sandringham estate in Norfolk, eastern England, ahead of the 4.30pm (1530 GMT) service.

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Royal Christening of Princess Charlotte

William and Kate walked to the service from a nearby royal residence with Charlotte and her brother George, giving the public their second glimpse of the little princess since she appeared on the steps of a London hospital after her birth on May 2.

Charlotte arrived for the ceremony in a vintage pram used by Queen Elizabeth for her own children in the past, pushed by her mother Kate, who wore an elegant cream outfit and hat.

"When I found out the christening was happening while we were here I knew I just had to be there," said Laurie Spencer, 52, from Florida, who gave up a ticket to the British Grand Prix to join the crowds.

Prime Minister David Cameron joined in the festivities, writing "My best wishes to the Duke and Duchess of Cambridge on Princess Charlotte's Christening today" on his Twitter page.

Archbishop of Canterbury Justin Welby, the spiritual head of the world's Anglicans, performed the baptism, using the ornate silver gilt Lily Font that is part of the crown jewels and pouring holy water from the River Jordan on the baby's head.

The fourth-in-line to the throne wore a replica of the lace and satin christening gown made for queen Victoria's eldest daughter in 1841.

Prince George, who turns two later this month, wore red shorts and a white embroidered shirt.

Three kings, five godparents

Three future kings -- Charles, William and George -- attended the ceremony, which was performed using a font from Victoria's reign.

Other guests included the 89-year-old queen and her husband Prince Philip, plus Kate's parents, Carole and Michael Middleton.

William and Kate announced early Sunday that Charlotte would have five godparents, including William's cousin Laura Fellowes and Kate's cousin Adam Middleton.

The others were Kate's friend Sophie Carter, and two close friends of William's, James Meade and Thomas van Straubenzee.

The Duke and Duchess of Cambridge have said they want their children to have relatively normal upbringings and have closely guarded their privacy, bringing them up in the secluded mansion Anmer Hall, close to the church.

Charlotte's christening was in sharp contrast to their lavish 2011 wedding, which was shown live across the world, and to the media frenzy surrounding the birth of their two children.

Though the service was conducted behind closed doors, it was to be documented by celebrity photographer Mario Testino, who was close to William's late mother Diana and took some of the most famous shots of her in 1997.

The service comprised two hymns, one lesson and two anthems, according to a statement from Kensington Palace.

The hymns were "Praise to the Lord, The Almighty" and "Come Down, O Love Divine" while the lesson was from Matthew 18, verses 1-5 and read by new godparent Meade.

The guests and members of The Sandringham Church Choir joined in with anthems "I Will Sing With The Spirit" and "God Be In My Head," both by John Rutter.

The service also included music from Vaughan Williams and Handel.

Afterwards guests enjoyed tea and cake at Sandringham House, the queen's nearby country retreat, including slices of christening cake -- cut from a tier of William and Kate's 2011 wedding cake.