Amazon US has launched a new delivery service based on the Uber concept.

Flex is a new means of the company making urgent deliveries to online shoppers. It is being launched on a trial basis in Seattle.

Like Uber, Flex will use private contractors who can register for freelance delivery work. Candidates must have a smartphone, a reliable vehicle and are subject to a background check.

If the concept works, it will be expanded into Manhattan, Baltimore, Miami, Dallas, Chicago and other markets.

“There is a tremendous population of people who want to work in an on-demand fashion,” Dave Clark, Amazon senior VP of worldwide operations, told the Wall Street Journal. “This is another opportunity for people to work with the company.”

“You can work as much or as little as you want,” the Amazon site promoting the concept to would-be drivers explains.