Shoppers swarmed to Karen Walker's online site after the Duchess of Sussex took her first steps on New Zealand turf wearing the branded trench coat.

The New Zealand designed tailored coat with double-breasted front with a price tag of $975 was not available until mid-November but pre-sale orders were sold within a few hours of Meghan's debut.

Karen Walker communications manager Jiali Yang said 75 per cent of these orders would be shipped to the US, and the rest would go to the UK, Australia and within New Zealand.

Designer Karen Walker said this trench coat was one of the brand's most beloved silhouettes.

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"It first appeared, in classic tan trench coating, in one of our shows at London Fashion Week in 2004. Since then we've refreshed and revisited it many times and it continues to be a favourite.

"Her Royal Highness looks very chic and we're delighted that she's chosen to wear Karen Walker once again," Walker said.

It was the fifth item Meghan has showcased on the royal tour.

She wore the brand's black Northern Lights sunglasses and a pair 9ct gold stud earrings on two separate royal engagements during her official visit to Australia with her husband Prince Harry.

In the 19 hours since the spotting of the sunglasses, the Karen Walker website sold more than seven times the number of units it sold the month previously - most orders came from overseas.

On another official outing to Bondi just days earlier the duchess wore Karen Walker's temptation earrings priced at $399.