Australia Post is celebrating the birth of His Royal Highness Prince Louis of Cambridge with the release of a new commemorative stamp.

Prince Louis Arthur Charles was born on 23 April at 11.01am BST, weighing eight pounds, seven ounces (3.83 kilograms).

The commemorative stamp features the royal newborn as he was introduced to the world, in the arms of his proud parents, Their Royal Highnesses the Duke and Duchess of Cambridge, on the steps of St Mary's Hospital in London.

The design is a similar style to the stamps used to commemorate the birth of his siblings, HRH Prince George in 2013 and HRH Princess Charlotte in 2015.

"Australia Post is thrilled to celebrate the birth of a baby boy to the Duke and Duchess of Cambridge and a new brother to his two older siblings," Australia Post Philatelic Manager Michael Zsolt said.

"We have a proud history of honouring the royal family and we expect this new stamp will be well received by collectors and followers of special events."

Prince Louis's birth was announced by a town crier outside the hospital, and later that day, according to tradition, two footmen placed the official declaration of the birth on an easel outside Buckingham Palace. Flags were also raised at Buckingham Palace and Windsor Castle to mark the birth of the new prince.

Prince Louis is fifth in line to the British throne, after his grandfather, Prince Charles; his father, Prince William; and his two siblings, Prince George and Princess Charlotte.

Jo Muré of the Australia Post Design Studio designed the stamp, which features gold-coloured ink through the typography and frame to emphasise the royal theme.

The stamp issue is available from 3 July 2018 at participating Post Offices, via mail order on 1800 331 794 and online at auspost.com.au/stamps while stocks last.