In a few years, ordering that boxed DVD set off Amazon.com could be even more tempting.

The company is developing a self-guided drone that would get packages to customers in half an hour or less, The Associated Press reported.

The Prime Air unmanned aircraft project is in the early stages in Amazon's research and development labs and could happen in the next four or five years, according to Amazon CEO Jeff Bezos.

Appearing on CBS' "60 Minutes," which first reported the project on Sunday, Bezos said the drones look like something out of science fiction but can be used to make deliveries.

The proposed flying drones wouldn't need humans controlling them from another location; instead, they would follow a set of GPS coordinates and deliver packages that weigh less than 5 pounds. About 86 percent of the items delivered by Amazon fit into that range, according to the AP.

The robot delivery machines face technical and legal obstacles. They would have to be designed to navigate roads and skies without crashing into anything, and as with driverless cars, liability is an issue: Who is responsible if there's an accident?

The biggest challenges are developing a collision avoidance system and getting the delivery system approved, said Darryl Jenkins, a consultant who formerly worked in the commercial airline industry and now focuses on drones.

Jenkins wondered who would insure the deliveries, who would recharge the drone's batteries and how many deliveries a drone could make before needing to be serviced. But he seemed to have confidence in Bezos' ability to follow through on the venture.

''Jeff Bezos might be the single person in the universe who could make something like this happen,'' Jenkins said. ''For what it worth, this is a guy who's totally changed retailing.''

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