After watching the number of confirmed coronavirus cases in the Los Angeles area escalate in the previous 24 hours and braving a few trips to grocery stores in person, Cindy Wu decided to schedule food delivery online, but that was no easy task.

"There was just no availability for food delivery on the websites of a lot of the major grocery outlets," said Wu, a resident of Alhambra, California. She is a member of Amazon Prime and has been trying for a week to book a delivery slot on Amazon Fresh. By the time she got a slot, half of the items in her online cart were no longer available.

The demand for grocery delivery is facing a crunch as cities and states across the US mandate or recommend people stay at home, and more consumers choose to have groceries delivered to their doors instead of risking exposure in public.

A quick search recently on the grocery delivery service Instacart revealed that no delivery options were available for the next three days for an address in Arcadia, California, near Alhambra. A message on Shipt asked the customer to "check back later" as no more delivery windows were available on Friday to the same address.

On the website of Vons, a Southern California supermarket chain with some locations in Nevada, delivery options for the next three days have all been unavailable.

Amazon Fresh had this message displayed on its front page: "Inventory and delivery may be temporarily unavailable due to increased demand. New windows are released during the day."

"It feels like we are essential to so many Americans — millions and millions around the country who are depending on Amazon and other services like it to deliver things that they might otherwise have felt comfortable getting at a physical store," said Jay Carney, senior vice-president of global corporate affairs at Amazon, to CNN in a recent interview.

"Amazon's a big e-commerce company, but e-commerce is still only about 10 or 11 percent of retail," he said. "During this crisis, I think people are relying on home delivery, getting things at their doorsteps, and that's why we have to call on our employees to just do heroic things, to work really hard, to add hours and then to hire more, just get Americans what they need."

To cope with skyrocketing demand, Amazon is temporarily prioritizing the shipment of medical supplies, household staples and other in-demand products, but it is also limiting the purchase quantities of those items.

Some Amazon warehouse workers in Staten Island, New York, staged a walkout Monday asking for better pay and safety protections after a worker there tested positive for COVID-19.

On Wednesday, a similar protest took place at an Amazon warehouse in Michigan, after an employee tested positive for the infectious virus.

The company said it has "taken extreme measures to keep people safe, tripling down on deep cleaning, procuring safety supplies that are available, and changing processes to ensure those in our buildings are keeping safe distances."

The e-commerce giant also said it is hiring for 100,000 new full- and part-time positions in its fulfillment centers and delivery network across the US, as well as adding an additional $2 an hour to the current hourly rate for employees in the US through April.

San Francisco-based Instacart said it has seen the highest customer demand in the history of the company.

"In the last few weeks, the company has seen order volume grow by more than 150 percent year-over-year, with average customer basket size also increasing by 15 percent," the company said in a statement.

"Based on the current surge in demand, customers can expect to see delivery availability vary across stores during the busiest request windows," it added. It encouraged customers to check their app frequently for available delivery times.

Instacart found itself in the spotlight last week when some of its workers organized a nationwide strike to demand better health protections and hazard pay of $5 per order.

The company said Thursday that it will supply its full-service employees free health and safety kits containing reusable cloth face masks, hand sanitizer and thermometers beginning next week. It also said it is launching a COVID-19 resource center to provide information for employees and customers.

Last week, Instacart announced plans to hire 300,000 new full-service employees over the next three months in respond to increased demand. In the week since that announcement, 250,000 new people have signed up, and 50,000 of them have already started work.

The company said it also has increased paid sick leave to 14 days for workers in quarantine and has increased bonus payments.

In an emailed statement to China Daily, a spokesman for the Boise, Idaho-based Albertsons Cos Inc, the parent company of Vons, said that its delivery and drive-up services have experienced higher-than-usual demand.

"As we add open slots for delivery and pickup, they are being reserved quickly by customers," the spokesman said.

The company is hiring 30,000 new employees, including delivery drivers and personal shoppers, to help meet the demand. It is also implementing a series of new measures to ensure the safety of customers.

For example, e-commerce team members are washing their hands and using sanitizer before every order. The company also has implemented "contact free" delivery procedures so that drivers can sign for customers after completing an ID check, if necessary.

A spokeswoman for Walmart, the world's largest retailer, told China Daily that the US multinational company is "seeing an increase in the number of orders coming in for our pickup and delivery services along with customers in our stores".

"We're offering time slots to customers for as soon as the same day and up to one day in advance, rather than time frames further out," she added. "This is a shorter window than we typically offer, but it will allow us to better serve our customers during this busy time."

Walmart said it is taking the temperature of employees as they report to work and is making masks and gloves available for them, as supplies permit. It also has enacted "no-contact" delivery and pickup options and will continue to promote social distancing.

Minneapolis, Minnesota-based Target Corp, which owns Shipt, said Thursday that it will limit customer traffic in all of its stores to promote social distancing, as of Saturday.

According to the marketing research firm Nielsen, only 4 percent of grocery sales in the country came from online purchases last year. As of March 15, downloads of the Instacart app were up 218 percent over last year, and Walmart's grocery app was up 160 percent. Data show that many new online subscribers are over the age of 60, researchers said.

In addition, online purchases of consumer packaged goods (CPG) — items depleted by consumers and replaced on a frequent basis, such as food, beverage and cleaning products — have undergone some dramatic changes during the outbreak.

In the two weeks ended March 21, about 35 percent more people had shopped online for CPG items compared with a typical week.

In addition to grocery items, consumers also are struggling to get their hands on personal protective equipment such as masks and gloves.

Jackie Wei, CEO of Sanberd Inc, a company in Walnut, California, that focuses on international e-commerce and overseas warehousing and sources its materials from suppliers in China, said these products usually are sold out within two hours after appearing on shelves online.

Wei's company maintains storefronts on e-commerce platforms including Amazon, Wish and Jumia. He said the pandemic has brought surprising sales surges.

Sales of car components increased 30 percent to 50 percent, Wei noted. Small home appliances, such as coffee makers, bread makers and smart trash cans, spiked 50 percent in sales. Fitness tools are popular among consumers, as well.

"It's possible that people have more time on their hands now to fix their cars and maintain their households and bodies since they work from home," he said.

Although most factories in China have resumed operations, restrictions on air-cargo flights are still causing some disruptions, he said.

The majority of the world's food supplies are transported via ship. However, both the cancellation of sailing routes and the reduction of air routes during the pandemic are disrupting the global supply chain, experts said.

Rules governing port access differ from country to country, and sometimes even within countries, making it difficult for ship owners to plan routes, Guy Platten, secretary-general at the International Chamber of Shipping, told CNN. That could snarl food supply chains, particularly for time-sensitive fresh produce, he added.