The world's biggest retailer is accelerating efforts to "combine our digital and physical assets to make our shipping simple and easy for customers," chief executive Doug McMillon said in a statement.

"Our customers have choices, and we have to earn their business with every interaction."

Wal-Mart has been pumping funds into improving its in-store experience, upgrading stores and boosting worker pay, at the same time that it builds out its e-commerce business.

The costs of those initiatives have pressured earnings in recent quarters, and the company reported earnings of $3.0 billion in the first quarter of fiscal 2018, down 1.3 percent from the year-ago period. Revenues were up 1.4 percent at $117.5 billion.

But the initiative has produced gains in comparable store sales in the US, a closely-watched benchmark that rose 1.4 percent in the first quarter.

E-commerce sales surged 63 percent and merchandise volume saw a 69 percent jump.

Analysts at Global Data Retail said Wal-Mart's sharp focus on keeping prices down in grocery was winning some customers back and described growth in e-commerce as evidence of a business "in the ascendancy."

"Overall, this is an encouraging start to the year for Walmart," GlobalData Retail said in a research note. "This is one US retailer that is ahead of the curve in responding to the evolving landscape."

Shares of Wal-Mart rose 1.9 percent to $76.56 in mid-morning trading. In contrast, Macy's, Nordstrom and Dick's Sporting Goods all plunged after their earnings reports.

Wal-Mart has boosted its online offerings to 50 million items, up five fold from a year ago, said Marc Lore, president and CEO, Walmart eCommerce US.

The company introduced free two-day shipping for orders over $35 and discounts on non-store products if a customer picks it up at a store, an effort to exploit its network as it competes with Amazon and others.

"There's more product to buy, you're able to get the product quicker," Lore said on a conference call with reporters. "The overall experience is improving."

The gains followed a number of Wal-Mart acquisitions over the last year, although executives described the majority of the growth as "organic."

Wal-Mart's financial reports do not break out revenues for e-commerce sales.

Chief financial officer Brett Biggs said e-commerce is "still fairly small" within Wal-Mart's US business and there was no immediate plan to disclose more details about the business.