AUSTRALIAN shoppers are in the grip of "Zara fever", with the frenzied Sydney launch the biggest ever for the Spanish clothing giant.

The opening of Zara has also boosted sales within the new Westfield Sydney, bucking the trend in the slump faced by shopping centres and retailers across the country.

Customers repeatedly cleared the shelves of Zara when it opened on Wednesday, with many queuing outside for hours to get in.

Within three minutes of the fast-fashion icon opening at 9am, 80 per cent of the stock had been sold. Visiting Spanish executives were forced to work on the floor, de-tagging outfits and replenishing merchandise.

Zara's chief communications director Jesus Echevarria said: "I've never seen anything like it. We've had great launches before but this is the biggest. Customers showed so many signs of affection and gratitude that we are all impressed."

The seemingly unstoppable growth of the almost 50-year-old company comes two years after Inditex overtook US chain Gap to become the world’s largest clothing retailer and five years after it surpassed H&M to take the top spot in Europe.

Loved by fans of fast-fashion, the key to Inditex’s success lies in its remarkable geographic diversification in recent years and a business model that has allowed it to put the latest fashions in its stores at breakneck speed.

“The success of the model lies in being able to adapt what you’re offering in the shortest time possible to what clients want,” says an Inditex spokesperson. “For Inditex, time is the principal factor to take into account, more so than the costs of production.”

Almost all the phases of developing and selling a new product are carried out in-house — from design and production to logistics and sales – and shop staff are encouraged, even expected, to keep Inditex designers in touch with any fashion trends as soon as they spot them.

Inditex has managed to get so far, so fast largely through the use of innovative management and logistics techniques, which have now become the subject of studies in business schools around the world.

For a company which spends very little on advertising, its shops have always been its principal marketing tool. Many are purpose-built to look like fashion boutiques, located on prime real estate in city centre high streets and malls around the world.