The world's largest retailer hopes to bolster online sales and go head to head with competitors such as Amazon, Target and Kroger in the growing grocery delivery business.

Walmart, the biggest private-sector employer in South Carolina, announced Wednesday it will expand its web-based service to more than 100 metro areas of the U.S., covering 40 percent of U.S. households, by the end of the year.

The delivery option is now offered in six markets — Dallas, Denver, Orlando, Phoenix, Tampa and San Jose. The expansion cities were not identified. They will be announced as they come online during the year, according to a Walmart spokesman.

The retailer charges a $9.95 fee for its grocery delivery service and requires a minimum order of $30.

In another effort to boost sales, the retailer said earlier this year it planned to accelerate its online grocery business this year by adding 1,000 stores where customers can place orders on the Internet and pick up the goods at nearby stores.

The service is now available at 1,200 locations.

The company said 90 percent of Americans live within 10 miles of a Walmart store. It estimated more it draws about 150 million shoppers each week.

The home-delivery expansion "gives us a unique opportunity to make every day a little easier for busy families," said Tom Ward, vice president of digital operations for Walmart U.S.

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Walmart's announcement comes after Target launched home delivery through its acquisition of same-day delivery service Shipt in select cities, including Charleston, in February. Kroger on Monday said that it would increase the number of cities where it offers home delivery of groceries through Instacart, also a same-day service.

The moves come nearly a year after online retail giant Amazon purchased upscale food chain Whole Foods.

Walmart has more than 32,000 employees at 123 stores in South Carolina, including Sam’s Club outlets. The company's 16 locations in the Charleston region employ about 3,650 workers.

Reach Warren L. Wise at 843-937-5524. Follow him on Twitter @warrenlancewise.