Nasa chiefs have said the SpaceX launch that was scheduled for Wednesday had to be delayed over concerns that the launch could trigger lightning.

Looming rain and thunderstorms meant that the first launch of astronauts from US soil in nine years had to be aborted just minutes before lift-off.

Robert Behnken and Douglas Hurley were due to travel to the International Space Station (ISS) on a rocket and capsule system built by billionaire entrepreneur Elon Musk’s firm SpaceX.

An estimated 1.7 million people from around the world tuned in to the launch from The Kennedy Space Centre in Florida.

However as the weather conditions continued to worsen, Nasa and SpaceX decided to “scrub” the mission for safety reasons, less than 17 minutes before the Falcon 9 rocket was due to take off.

Nasa administrator Jim Bridenstine said the decision was made because there was “simply too much electricity in the atmosphere”.

He added: “There wasn’t really a lightning storm or anything like that, but there was concern that if we did launch it could actually trigger lightning.”

“I know there is a lot of disappointment today. The weather got us.”

The launch date has now been moved to Saturday at 8:22 pm UK time.

Mr Bridenstine added: “But I also wanted to say this was really a great day for Nasa it was a great day for SpaceX. I think our teams worked together in a really impressive way, making good decisions all along.

“We have a lot to look forward to. In just a few short days on Saturday afternoon we are going to do it again.

“Here is what we know – we are going to launch American astronauts on an American rocket from American soil. We are going to do that. We are very close.”

While the conditions were improved shortly after the launch was scrubbed, the teams went ahead with the postponement because the launch window was instantaneous, which meant the spacecraft would have had to leave on time to rendezvous with the space station.

Mr Behnken and Mr Hurley had to remain strapped in their seats until all the fuel in their rocket was unloaded and the emergency escape system was disarmed.

Before exiting the Crew Dragon capsule, Mr Hurley, who is the commander of the spacecraft, said: “We could see some raindrops on the windows and just figured that whatever it was, was too close to the launch pad at the time we needed it not to be.

“Understand that everybody’s probably a little bit bummed out. That’s just part of the deal.”

British astronaut Tim Peake said it was a shame that the SpaceX launch was scrubbed but added “the rules are there in the interest of safety”.

The mission, named Demo-2, would have seen SpaceX become the first private company to send astronauts into space.

Nasa and SpaceX joint mission
Douglas Hurley, left, and Robert Behnken on their way to board the SpaceX Crew Dragon (Bill Ingalls/Nasa)

Since ending its Space Shuttle programme in 2011, Nasa has depended on Russia’s space agency Roscosmos to transport its astronauts to the space station.

In 2014, Nasa awarded SpaceX and Boeing contracts to provide crewed launch services to the space station as part of its Commercial Crew Program.

According to Nasa, the aim of the Demo-2 mission to show SpaceX’s ability to ferry astronauts to the space station and back safely.

It is the final major step required by SpaceX’s astronaut carrier, the Crew Dragon, to get certified by Nasa’s Commercial Crew Program for more long-term manned missions to space.