Updated: As new stores designate shopping hours for seniors and vulnerable customers, we will add to our list.

Some retailers are setting aside time for their most vulnerable customers to shop.

Acknowledging that older adults and persons with underlying health conditions are more susceptible to COVID-19, a growing number of stores are dedicating time or opening earlier for senior shoppers and other at-risk groups.

Because of panic shopping, which has left many store shelves empty, at-risk groups including seniors have had difficulty getting supplies.

Costco Wholesale Club started a twice-weekly senior hour March 24 for Tuesdays and Thursdays and added Wednesdays as a third day. It's also allowing “those with physical impairments” to participate.

Walgreens also has a Tuesday weekly senior hour from 8 to 9 a.m., open to caregivers and immediate families, as well.

Through April 28, Walmart stores will host an hour-long senior shopping event every Tuesday for customers 60 and older. The designated hour will start one hour before the retailer's 5,000-plus U.S. stores open.

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Albertsons, which has 2,200-plus stores under banners including Safeway, Acme and Vons, says it is reserving two hours every Tuesday and Thursday morning for vulnerable shoppers, including senior citizens, pregnant women or those with compromised immune systems "who have been advised to avoid leaving home as much as possible."

Until further notice, all Whole Foods Market stores in the U.S. and Canada will let customers who are 60 and older shop one hour before opening to the public. The company, which is owned by Amazon, has approximately 500 stores throughout the U.K., Canada and in 42 U.S. states.

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Target has expanded its weekly hour once a week to twice a week for elderly and vulnerable shoppers. On Tuesday and Wednesday mornings, the first hour at the retailer's more than 1,800 stores nationwide will be reserved for these shoppers.

Dollar General designated the first hour at its more than 16,000 stores in 44 states as open daily to senior shoppers.

Several small and regional grocery store chains also are looking to help, though most retailers are not requiring identification or proof of age and are only "encouraging" other shoppers to plan around these windows.

Some experts say they are concerned about having a large number of seniors congregate together. Alysa Krain, an infectious disease doctor who specializes in geriatric medicine at the University of Pennsylvania’s Perelman School of Medicine, told the Washington Post that the special hours make her nervous.

“It was a good idea in general, but it’s a little bit dangerous if it’s not controlled,” Krain told the Post.

Stores helping elderly, vulnerable

Albertsons: From 7 to 9 a.m. on Tuesday and Thursday, the company is reserving time for "those vulnerable shoppers who must leave home to obtain their groceries, unless otherwise locally mandated." Find the full list of Albertsons companies stores here.

Aldi: On Tuesdays and Thursdays, stores will open at 8:30 a.m. and "reserve the first hour of business for vulnerable shoppers." The discount grocer said this includes "senior citizens, expectant mothers and those with underlying health concerns."

Balducci’s: With locations in Virginia, Maryland, New York and Connecticut, the grocer is reserving the first hour of shopping for the elderly and high-risk guests.

Bashas' Supermarkets: The company's stores including Bashas', Food City and AJ's grocery stores will open from 5 to 6 a.m. Wednesdays for anyone 65 and older, reported the Arizona Republic, which is part of the USA TODAY Network. The hour for Bashas' reservation stores is from 6 to 7 a.m. Shoppers will be required to show valid identification at the store. If a caretaker is needed, one can shop with the senior but cannot shop for themselves.

Big Lots: Stores are reserving first hour of each day for senior citizens and “those most vulnerable to this virus,” CEO Bruce Thorn said in an email to shoppers.

BI-LO: All Southeastern Grocers stores, including BI-LO, Fresco y Más, Harveys Supermarket and Winn-Dixie, are dedicating an hour for seniors and high-risk customers to shop from 8 to 9 a.m. Monday through Friday. The company said in a statement it “asks all customers to respect this time given to the elderly and other high-risk community members to allow them the comfort of purchasing necessary products in a safe environment.”

BJ's Wholesale Club: Starting March 22, all locations will open one hour early every day for members who are age 60 or older. This opening hour will be from 8 to 9 a.m. daily and there will be a designated entrance.

Costco Wholesale Club: The retailer is now offering three senior shopping hours a week and is allowing “those with physical impairments” to also participate. “On Tuesdays, Wednesdays, and Thursdays, Costco warehouses will open from 8 to 9 a.m. for members ages 60 and older, and for those with physical impairments,” Costco’s website notes.

Dollar General: The Goodlettsville, Tennessee-based discount chain announced it is dedicating the first hour in its more than 16,000 stores in 44 states to help senior shoppers "avoid busier and more crowded shopping periods." The retailer said in a tweet that it wasn't "qualifying a specific age" for the set-aside time.

DoorDash: The on-demand delivery company is "powering free delivery from more than 2,000 grocery store locations nationwide by waiving delivery fees for those 60 years of age and over," DoorDash said in a blog post. Hy-Vee, Woodman’s, Kowalski’s Markets and hundreds of independent grocers and specialty food shops like Piggly Wiggly, LifeThyme Natural Market, Le District, and Matherne’s are included and directions on how to get the discount are on the blog post. Mercato.com, which has more than 900 participating stores, also is offering free delivery with DoorDash with promo code OVER60, according to a news release.

Fareway Meat & Grocery: Starting March 18 and until further notice, stores will open to shoppers 65 and older, expecting mothers and those with "increased susceptibility to serious illness" from 8 to 9 a.m. Monday through Saturday. Stores will be open from 9 a.m. to 7 p.m. for the public.

Fresh Market: The grocer, which has 159 stores in 22 states, is reserving the first hour stores open, from 8 to 9 a.m., for "seniors and those most at risk" Monday through Friday.

Fresco y Más: Stores are dedicating an hour for seniors and high-risk customers to shop from 8 to 9 a.m. Monday through Friday. The company said in a statement it “asks all customers to respect this time given to the elderly and other high-risk community members to allow them the comfort of purchasing necessary products in a safe environment.”

Food Town: The Texas-based retailer says to "help support the shopping needs of the elderly in our community," stores will open from 7 to 8 a.m. to allow those 65 and older to shop in a less-crowded environment. Access to the store during the hour will require a government-issued state ID or Texas driver's license.

Gelson's: Starting Wednesdays, seniors 65 and older can shop from 7 to 8 a.m. "You may be asked for ID," the California grocer said on its website.

Giant Food: Starting March 20, the chain with stores in Washington, D.C., Maryland, Virginia and Delaware will offer "dedicated shopping hours for senior citizens 60-and-older and individuals with compromised immune systems," Giant Food said in a release. The dedicated time is from 6 to 7 a.m. "every day of the week for this vulnerable population to shop and practice social distancing."

Jersey City: In Jersey City, New Jersey, grocery stores will allocate two hours every morning, from 9 to 11, specifically for elderly, disabled and pregnant shoppers, Mayor Steven Fulop said. The rule started Tuesday and applies to grocery stores that have three or more cash registers.

Harveys Supermarket: All Southeastern Grocers stores, including BI-LO, Fresco y Más, Harveys Supermarket and Winn-Dixie, are dedicating an hour for seniors and high-risk customers to shop from 8 to 9 a.m. Monday through Friday. The company said in a statement it “asks all customers to respect this time given to the elderly and other high-risk community members to allow them the comfort of purchasing necessary products in a safe environment.”

Kings Food Markets: With locations in New Jersey, New York and Connecticut, the grocer is reserving the first hour of shopping for the elderly and high-risk guests.

Mother’s Markets: The California-based company is starting "Safe Shop Wednesdays” and is opening from 6 to 7 a.m. every Wednesday for “elderly, disabled, those with compromised immune systems, chemo patients, etc.” It's also offering free home delivery for the high-risk groups with promo code FREE4SENIORS.

Northgate González Market: The Southern California Latino market has started a special hour of shopping for the disabled and seniors 65 and older from 7 to 8 a.m. at its 41 locations.

Publix: Starting March 24 and until further notice, Publix is designating Tuesday and Wednesday mornings from 7 to 8 a.m. for seniors 65 and over, the company said Thursday. Pharmacies also will open at 7 a.m. "Tuesdays and Wednesdays to serve our senior population," the Florida-based retailer said.

Sam's Club: The wholesale club introduces twice-weekly special hours for seniors, people with disabilities and those with compromised immune systems, and a "Shop from Your Car" concierge service starting Thursday, March 26. The special hours will be held every Tuesday and Thursday from 7 to 9 a.m. "until further notice."

Safeway: From 7 to 9 a.m. Tuesday and Thursday, the company is reserving time for "those vulnerable shoppers who must leave home to obtain their groceries, unless otherwise locally mandated."

Schnucks: Starting March 18 and continuing indefinitely, Schnucks is reserving the first hour of each day – from 6 to 7 a.m. – for shopping by seniors aged 60 and above, and for those who are most at risk of COVID-19, the grocer announced.

Sedano's Supermarkets: Starting Thursday, the Florida-based chain's 35 locations will open from 7 to 8 a.m. for seniors 65 and older and "the immunocompromised members of our communities," the company said.

Smith's Food & Drug Stores: Smith’s will dedicate the first hour on Mondays, Wednesdays and Fridays from 7 to 8 a.m. "solely to the shopping needs of senior citizens until further notice," the company wrote in a Facebook post.

Stop & Shop: Starting March 19, the retailer, which has more than 400 stores throughout Massachusetts, Connecticut, Rhode Island, New York and New Jersey, will give shoppers 60 and older 90 minutes to shop each morning from 6 to 7:30 a.m., according to the Asbury Park Press, part of the USA TODAY Network. Stop & Shop said the dedicated time better enables social distancing and there would be a designated entrance for seniors.

Target: The retailer has expanded its weekly hour once a week to twice a week for elderly and vulnerable shoppers. On Tuesday and Wednesday mornings, the first hour at the retailer's more than 1,800 stores nationwide will be reserved for these shoppers and Target is "encouraging other guests to plan their shopping trips around this time frame."

Trader Joe's: Starting March 23, the first hour of daily shopping will be reserved for senior customers, from 9 to 10 a.m. The company didn't specify the age range of seniors, which is generally considered to be 65 and older, but it varies by company.

Vallarta Supermarkets: Starting March 18, all 50 locations will be open from 7 to 8 a.m. for shoppers 65-plus, pregnant women and those with disabilities, the grocer said in a Facebook post.

Walgreens: The drugstore chain has designated Tuesdays as "Seniors Day." The company's locations will be reserved for seniors, their caregivers and their immediate families from 8 to 9 a.m. Tuesdays. Customers 55 years and older will get special discounts on Tuesdays.

Walmart: From March 24 through April 28, Walmart stores will host an hour-long senior shopping event every Tuesday for customers 60 and older, which will start one hour before stores open. Checking IDs is at the store's discretion, Walmart told USA TODAY.

Whole Foods Market: Until further notice, all Whole Foods Market stores in the U.S. and Canada will let customers who are 60 and older shop one hour before opening to the public.

Winn-Dixie: All Southeastern Grocers stores, including BI-LO, Fresco y Más, Harveys Supermarket and Winn-Dixie, are dedicating an hour for seniors and high-risk customers to shop from 8 to 9 a.m. Monday through Friday. The company said in a statement it “asks all customers to respect this time given to the elderly and other high-risk community members to allow them the comfort of purchasing necessary products in a safe environment.”

Contributing: David P. Willis, Asbury Park Press; Anthony Zurita, NorthJersey.com; Alyssa Stoney, Arizona Republic; Donnelle Eller, Des Moines Register

Follow USA TODAY reporter Kelly Tyko on Twitter: @KellyTyko