Walmart is working with delivery service Postmates to bring online grocery orders to more shoppers' homes, with the goal of reaching more than 40 percent of U.S. households.

The partnership will roll out in Charlotte, North Carolina, the companies announced Tuesday, and will expand nationwide in coming months.

Having a grocery delivery service is increasingly important as more shoppers place their orders online while relaxing on the couch. Industry experts say they expect a continued uptick of activity in the space as delivery becomes faster and more efficient.

In March, Walmart announced plans to expand its grocery delivery business for online orders to 800 stores by year's end. The retailer at the time said it would be working with Uber and Deliv, among other partners, to provide transportation.

"We will ... reach as many households as we can," said Tom Ward, vice president of Walmart's U.S. digital operations. "We will leverage our footprint where it makes the most sense."

In working with Postmates, Walmart's personal shoppers will pull together items from online orders, which can then be delivered to homes the same day an order is placed. The minimum purchase amount is $30, not including a $9.95 delivery fee.

Amazon is also bulking up its delivery service for online grocery orders. Earlier this year, the e-commerce giant started delivering groceries from Whole Foods via its two-hour Prime Now platform.

Same-day delivery company Instacart has also been signing more deals with retailers including Albertsons, Kroger, Publix, Ahold Delhaize and HEB. Just last week it announced it had raised $150 million to help fund its aggressive expansion plans.