Online retail giant Amazon will base its new headquarters in New York City and Arlington, Virginia, located just outside Washington, the US capital.

The two new locations will together have about 50,000 employees, the company said on Tuesday. The company already employs several thousand people in the two areas. The firm will continue to have a base in Seattle.

"Amazon's investments in each new headquarters will spur the creation of tens of thousands of additional jobs in the surrounding communities," the company said in a statement, adding that recruitment will begin next year.

There have been concerns about the impact of Amazon's new bases on tight housing markets and transportation systems.

"New York City is about to get tens of thousands of new, good paying jobs and Amazon is about to meet the most talented work force in the world in one of the most diverse places on the planet," Mayor Bill de Blasio said on Twitter.

In a statement, Amazon said it would be receiving "a refundable tax credit through New York State's Excelsior Program of up to 1.2 billion dollars." Arlington and Virginia are offering "performance-based direct incentives of 573 million dollars."

The company also said Nashville, Tennessee will get a new Amazon centre, which will employ some 5,000 people.

Over 200 cities and communities originally offered to host the new headquarters, and they were pared down to 20 sites by the company in January this year.

The two locations revealed on Tuesday had longed been rumoured as the likely choice by Amazon, but the formal announcement puts an end to many months of speculation.