SpaceX successfully launched a secret US Air Force space plane on Thursday ahead of the arrival in Florida of Hurricane Irma.

Live images broadcast by the California aerospace company showed a Falcon 9 rocket carrying the unmanned X-37B drone lifting off at 10:00 am (1400 GMT) from NASA's Kennedy Space Center.

The recoverable first stage of the launch vehicle then landed at Cape Canaveral Air Force Station less than 10 minutes later.

There were concerns SpaceX, owned by Elon Musk, would be forced to postpone the launch as Hurricane Irma threatens to batter Florida.

But skies were clear Thursday and the company managed to complete the launch ahead of the expected weekend arrival of Irma, a powerful Category Five hurricane.

It was SpaceX's second mission for the Pentagon this year following a secret satellite launch in May and the private company's first launch of the X-37B.

Previous X-37B launches had been performed by the United Launch Alliance, a joint venture between Lockheed Martin and Boeing.

The X-37B, also known as the Orbital Test Vehicle (OTV), is one of two known craft of its type in the US Air Force's fleet and part of a classified program whose details are shrouded in secrecy.

A reusable shuttle, Thursday's launch is its fifth mission since its maiden flight in April 2010.

"The fifth OTV mission continues to advance the X-37B's performance and flexibility as a space technology demonstrator and host platform for experimental payloads," the Air Force said in a statement.

"This mission carries small satellite ride shares and will demonstrate greater opportunities for rapid space access and on-orbit testing of emerging space technologies."

On its last mission, the solar-powered X-37B stayed in orbit for 718 days before returning to land on May 7 -- longer than any of its previous flights.

Some 29 feet long (nine meters) and 15 feet (4.5 meters) wide, it resembles the space shuttle, the last of which flew in July 2011.