As the top of an hour approached, about 15 drivers began filing into Amazon's Prime Now hub in Minneapolis. The first eight lined up, then the others, as black carts with sealed brown bags were wheeled out to each of them.

The drivers, some of whom had left their cars running outside to keep them warm and get a head start on the one- to two-hour delivery window, scanned the bar codes on each package and then were off to courier them to various corners of the Twin Cities on Thursday morning.

This warehouse in an industrial area of southeast Minneapolis has been hopping since Amazon first opened it in October 2015. In fact, it has become so busy that the Twin Cities is now one of Amazon's top markets for Prime Now, its two-hour delivery service in more than 30 cities, a company spokeswoman confirmed.

The hub will be buzzing right up until the last hour of the holiday shopping season. While it usually ends deliveries at 10 p.m., Amazon has extended its hours until midnight on Friday night and Christmas Eve for last-minute purchases.

"We expect to be pretty busy," said Amazon spokeswoman Leah Bibbo. "You can imagine while people are wrapping gifts, you discover that a toy you bought needs batteries. Or maybe you have people over for the evening and you run out of eggnog."

The deadlines for free delivery of online orders for most other retailers has already passed. So the best option for last-minute shopping at those establishments is heading out to the stores in person.

While many shopping centers have extended hours this week in the final sprint to Christmas and Hanukkah, retailers are taking different approaches to their hours on Christmas Eve, which falls on a Saturday this year.

Minneapolis-based Target Corp. will keep its stores open until 10 p.m. or 11 p.m. for last-minute procrastinators that night, with a 6 p.m. deadline for placing online orders that can be picked up later in stores on Christmas Eve. Richfield-based Best Buy will close at 6 p.m., the same time as it did last year, with a 4 p.m. deadline for online orders to be picked up in stores.

Wal-Mart, which stays open all day on Thanksgiving, also will close at 6 p.m. on Christmas Eve, two hours earlier than last year.

"Our associates work hard all year to make this holiday season special for our customers, and we truly appreciate what they do every day," Judith McKenna, Wal-Mart's chief operating officer, said in a statement. "We also know that getting home on Christmas Eve to spend time with families is important. That's why this year we'll be closing at 6 p.m. on Christmas Eve."

In the last year or so, Amazon, which has been siphoning away customers from brick-and-mortar retailers, has been aggressively expanding its operations around the Twin Cities. Over the summer, it opened a sprawling, newly built fulfillment center in Shakopee where it has hired 1,500 employees and is already looking to recruit another 1,000 workers.

In recent weeks, Amazon quietly launched free same-day delivery in the Twin Cities to members of its $99-a-year Prime membership program, which already promises free two-day delivery on many items nationwide.

More than a million items are available for free same-day delivery through Amazon seven days a week on orders of at least $35.

On top of that, a smaller assortment — still tens of thousands of items — are available to Prime members for free delivery within two hours through the Prime Now app with a $20 purchase. Customers also can pay an extra fee of $7.99 to get deliveries within an hour. Amazon has also added other perks to the Prime Now service such as restaurant and alcohol delivery in the Twin Cities.

The one- to two-hour Prime Now orders are fulfilled through the 40,000-square-foot hub on Kasota Avenue in Minneapolis. Amazon contracts with drivers who use their own cars to deliver the packages, similar to how Uber and Lyft work.

"We have staffed up significantly for the holidays to make sure we can deliver orders to our customers," Bibbo said. But she declined to say how many drivers Amazon is working with in the Twin Cities.

Last year during the holidays, she said the Amazon Echo, Fire tablets, HDMI cables and pressure cookers were some of the top sellers on Prime Now locally.

Throughout the year, other items such as bananas, sparkling water, eggs and Gummy Bears are usually the most popular items, she said.

"At the beginning of December, popular items were things like toys and games for a family to play over the holidays," she said. "And then this week, the last week before Christmas, it's a lot more last-minute items, so party supplies, wrapping paper, host and hostess gifts as well and electronics."

In the Prime Now hub, a group of employees stand around computer screens monitoring orders. When a one-hour delivery order comes in, they call it out and a worker puts the items on a special cart with red and white tape on it to set it apart from other orders and get it out the door more quickly.

Workers carry handheld devices that tell them where to locate various items. They push around carts with empty brown paper bags, filling them with items they pick from the shelves.

In one corner, there are several racks of bananas with signs reminding the pickers not to select ones that have any brown spots on them. There's also a freezer section with a large selection of frozen pizza and other items that are placed in cold-pack bags.

In the back, there's an area for larger items such as 12-pack cartons of Diet Coke, Mountain Dew and La Croix water as well as other items that don't fit into bags such as TVs, printers and small appliances.

As they wait for their turn to make a delivery, drivers wait in the lobby where there's a TV and some tables and chairs.

On the wall that separates the waiting room from the warehouse, it says in large letters: "Work Hard. Have Fun. Make History."