Police have warned motorists of "significant congestion" In Westgate near the new Costco site which opened today.

The big box retailer opened this morning with queues out the door at Westgate ahead of its opening.

"Police would like to advise motorists of significant congestion around Fred Taylor Drive and Gunton Drive, Westgate.

Unless you are specifically travelling to the area, motorists are advised to take another route to get to their destination," police said.

A woman who arrived at Costco and joined the queue at lunchtime said it was taking about 40 minutes to reach the store's entrance.

The shopper said she arrived to join shoppers at 12.19pm to find the queue was beyond the end of the building.

Photos show a long line of shoppers snaking around the complex and carpark.

Image / Google

Costco Wholesale, founded in 1983, has stores in the United States, Puerto Rico, Canada, United Kingdom, Mexico, Japan, Korea, Australia, Spain, France, Iceland, China and via a majority-owned subsidiary in Taiwan.

The chain had stores in 828 locations at the end of last year of which 572 are in the US.

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The Auckland warehouse is a $100 million-plus membership store, costing $60/person or $55/business annually.

Costco's last annual report cited net sales for the 52-week fiscal year ending August 2021 totalling US$192 billion, up 18 per cent. Net income was US$5b, up 25 per cent. Revenue from membership fees rose 9 per cent to US$3.9b.

It buys most of its merchandise directly from manufacturers and its strategy is to provide members with a broad range of quality goods at prices consistently lower than elsewhere.