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Walmart’s announcement last month that it has started delivering groceries in a half hour in dozens of markets might look like just another move by the retailer to keep up with Amazon, which said only two weeks earlier it was expanding its own 30-minute grocery delivery service.

Look beneath the surface, however, and the race between the two retail giants to satisfy consumers' desire for speed exposes an emerging trend that could eventually have profound implications across the grocery sector, according to industry analysts.

Amazon and Walmart have long posed a threat to brick-and-mortar grocers online because of their vast reach and deep pockets. But as they build out their 30-minute offerings, they are taking away perhaps the top benefit grocery chains provide customers — convenience — said David Bishop, partner at grocery e-commerce consultancy Brick Meets Click.

Rapid delivery is “undercutting one of the core strategic advantages that regional grocers or supermarkets have historically enjoyed in the physical world, which is proximity to the customer,” Bishop said.