SpaceX, billionaire entrepreneur Elon Musk's private rocket company, was forced by foul weather to scrub a planned launch on Wednesday of two Americans into orbit from Florida, a mission that would be the first spaceflight of NASA astronauts from U.S. soil in nine years.

The countdown was halted 16 minutes and 54 seconds before the SpaceX Falcon 9 rocket was due to lift off from the Kennedy Space Center, propelling Doug Hurley and Bob Behnken on a 19-hour ride to the International Space Station, Reuters reported.

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Mission managers cited "a number of weather violations" for scrubbing the flight.

The next launch window is set for Saturday afternoon, when SpaceX will make a second attempt to send the astronauts into orbit aboard the company's newly designed Dragon Crew capsule.

The scrubbed launch came on a day with off-and-on rain over Florida. The National Weather Service had issued a tornado warning for the area. Mission managers were monitoring a number of ominous weather conditions, including the threat of lightning, even as crews began loading the rocket with fuel, when the countdown clock was stopped.

By then, Hurley, 53, and Behnken, 49, had already strapped into their Crew Dragon seats for a little more than two hours, after having made their way up a 265-foot-tall (80-meters) tower to the access bridge that leads to the capsule atop the Falcon 9 rocket.