She is satisfied with the delivery service in Hubei's smaller cities as well. Usually, within 30 minutes of placing the order, her food is delivered by people who are polite and helpful, she said. For example, they caution her if the drink is hot.

Such user experience and service quality have helped make takeout apps a mainstream business sooner than expected.

According to the latest annual report of Analysys, a Beijing-based consultancy, China's takeout apps netted sales of 45.78 billion yuan in 2015.

The market is expected to grow further in the next five years. In the last quarter of 2015, 67.7 percent of the business was from office-goers and 26.6 percent from university campuses. More than half of the orders were for less than 30 yuan each.

"App users are typically consumers living fast-paced lives. Businesses like restaurants can increase their profits by working with takeout apps," said Zhang Yan, vice-president of Baidu Takeout, which is among China's top food apps.

Its main customers are big city white-collar workers aged 25-40, a group less price-sensitive than others but valuing food safety and timely delivery, Zhang said.

The app mainly works with chain restaurants that ensure food safety and quality service. Its staff conduct spot checks from time to time and ask participating restaurants to rectify problems, if any.

"The takeout apps are bringing us more business. We mostly deliver lunchboxes and regular Chinese dishes," said Wang Jiuwei, in-charge of Jinbaiwan, a Beijing-based takeout chain known for its Peking duck delicacy.

One of Jinbaiwan's branches near the Beijing Railway Station gets between 400 and 500 delivery orders a day during weekdays. The restaurant had its own delivery team until 2015 when the function was outsourced to Baidu Takeout.

To prepare its packaged lunches, Jinbaiwan uses pan-like machines that can process about 1 kg of food at a time if all ingredients are in place. They're easy to operate and save cooking time for the chefs.

That makes it easy to start an app-based takeout business that links physical business and e-commerce, and relies heavily on quick delivery, according to TianYu, the co-founder of Beijing-based restaurant Jacky's Kitchen.

"We attach great importance to taste, our performance-price ratio and customization of food, to ensure good user experience," said Tian, whose spicy seafood is ordered a lot on takeout apps.