Amazon.com is building a new air hub near Cincinnati to support a growing fleet of planes that can move inventory around the US so online shoppers get their orders quickly.

Amazon will invest $US1.49 billion ($1.96 billion) to build the facility on 900 acres (364 ha) at Cincinnati/Northern Kentucky International Airport, said Mindy Kershner, an airport spokeswoman.

The airport is located in Hebron, Kentucky, and is southwest of Cincinnati.

The e-commerce giant has 11 warehouses in Kentucky where inventory is stored, packed and shipped to customers ordering goods over the internet.

The air hub will support the 16 planes transporting Amazon inventory around the country.

Amazon last year signed agreements with two carriers to lease as many as 40 cargo planes to support its new Prime Air operation.

Cargo planes are one of the latest tools the Seattle retailer is using to control and improve delivery.

Other efforts include a mobile app for delivery drivers and increased trucking capacity.

The company already has a worldwide network of about 149 fulfillment centres and 20 sorting centres that handle online orders and it uses 45,000 robots.

Amazon will employ 2000 workers at the new facility when it opens.

Chief executive officer Jeff Bezos has pledged to hire 100,000 people in the US over the next 18 months.