Musk's SpaceX US satellite launch halted

Elon Musk's SpaceX has halted launch of a navigation satellite for the US military, postponing for at least a day the space transportation company's first national security mission for the United States.

SpaceX's Falcon 9 rocket, carrying a $US500 million ($A695 million) GPS satellite was due to take off from Florida's Cape Canaveral shortly after 1.30am AEDT on Wednesday but was stopped minutes before take-off.

"This abort was triggered by the onboard Falcon 9 flight computer," a SpaceX official narrating the launch sequence said, adding that SpaceX would attempt the launch on Wednesday morning.

SpaceX later tweeted that the Falcon 9 and payload remain healthy and cited an "out of family" reading on the rocket's first stage sensors for the delay.

A successful launch would be a significant victory for Musk, a billionaire entrepreneur who spent years trying to break into the market for lucrative military space launches, long dominated by Lockheed and Boeing Co.