A US military plane developed to fly anywhere in the world in an hour has gone missing on its second test flight.

The unmanned hypersonic plane developed for US defence research into super-fast global strike capability was launched atop a rocket overnight but contact was lost after the experimental craft began flying on its own, the Defense Advanced Research Projects Agency said.

There was no immediate information on how much of the mission's goals were achieved.

It was the second of two planned flights of a Falcon Hypersonic Technology Vehicle-2. Contact was also lost during the first mission.

The craft is part of a US military initiative to develop technology to respond to threats at 20 times the speed of sound or greater, reaching any part of the globe in an hour.

The HTV-2 is designed to be launched to the edge of space, separate from its booster and manoeuvre through the atmosphere at 21,000 kph before intentionally crashing into the ocean.

DARPA used Twitter to announce the launch and status of the flight.

The agency said the launch of the Minotaur 4 rocket was successful and separation was confirmed. It next reported that telemetry had been lost.

No further details were immediately reported. There was no immediate response to an email request to DARPA for information on the mission.

The HTV-2 is intended to put theory, simulations and wind tunnel experience to the test in real flight conditions at speeds producing temperatures in the thousands of degrees and requiring extremely fast control systems, according to DARPA.

The first HTV-2 was launched on April 22, 2010. It returned nine minutes of data, including 139 seconds of aerodynamic data at speeds between 17 and 22 times the speed of sound, DARPA said.

That craft detected an anomaly, aborted its flight and plunged into the ocean, the agency said.

- AP