A SpaceX Falcon 9 rocket carrying two veteran NASA astronauts has blasted off from the Kennedy Space Center in Florida in a historic first private crewed flight into space.

The two-stage SpaceX rocket with astronauts Robert Behnken and Douglas Hurley aboard blasted off smoothly in a cloud of orange flames and smoke from Launch Pad 39A for the 19-hour voyage to the International Space Station.

The first crewed flight from US soil since the space shuttle programme ended in 2011 had originally scheduled to launch Wednesday but was postponed because of poor weather just 17 minutes before lift-off.

Moments after the Dragon capsule separated from the second stage of the Falcon 9 rocket and made it into orbit, the crew were given a message from the team on the ground.

The Falcon 9's chief engineer said: "On behalf of the entire launch team, thanks for flying with Falcon 9  today. We hope you enjoyed the ride and wish you a great mission."

One of the crew replied: "Congratulations to you and the F9 team for the first human ride for Falcon 9 and it was incredible. Appreciate all the hard work and thanks for the great ride to space." 

Lift-off took place at 8.22pm Irish time from the Kennedy Space Center. Last night, a spokesperson said SpaceX was on the "correct trajectory" to reach the International Space Station.

Astronauts Robert Behnken (R) and Douglas Hurley on their way to the SpaceX Falcon 9 rocket 

The mission, named Demo-2, has made billionaire entrepreneur Elon Musk's SpaceX the first private company to send humans into space, ushering in a new era of commercial space travel.

The fuelling of the Falcon 9 rocket with rocket grade kerosene and liquid oxygen began 45 minutes before the scheduled blast-off of the Falcon 9 rocket and its Crew Dragon capsule.

US President Donald Trump and Vice President Mike Pence arrived at the test site shortly before lift-off. "It's incredible," Mr Trump said at the launch.

"I am thrilled to announce that the SpaceX Dragon capsule has successfully reached low-Earth orbit and that our NASA astronauts are safe and sound.

"With this action the decades of lost and little action are officially over. A new age of American ambition has now begun.

US President Donald Trump (R) and Vice President Mike Pence arrive to attend the SpaceX launch

"This is just the beginning," he said. "It's really something special."

"Space will be one of the most important things we have ever done," President Trump added, noting that "nobody does it like us".

Mr Pence told those gathered at the space centre: "Today, under this President, we begin a new mission. To return to the Moon and ultimately land American astronauts on the face of Mars."

SpaceX's 'Demo-2' mission is the first flight with astronauts on board the Crew Dragon capsule built by Elon Musk's commercial space company.

SpaceX conducted a successful test flight of Crew Dragon to the ISS in March 2019 with a sensor-laden mannequin on board named Ripley, after the character played by Sigourney Weaver in the 'Alien' movies.

Veteran astronauts Robert Behnken, 49, and Douglas Hurley, 53 are both are former military test pilots who joined NASA in 2000.

The pair, who have each flown on two space shuttle missions, had been in quarantine for more than two weeks before blast-off and were regularly tested for Covid-19.

The SpaceX Falcon 9 Crew Dragon Demo-2 is pictured shortly after blast-off

The length of the astronauts' stay aboard the ISS has not been determined yet but Crew Dragon can spend up to 114 days in space, or 16 weeks.

On arrival at the International Space Station, they will join the three other residents - NASA's Chris Cassidy and Russia's Anatoli Ivanishin and Ivan Vagner.

Astronaut Doug Hurley waves en route to Launch Complex 39A at the Kennedy Space Center 

NASA chief Jim Bridenstine has said they may return to Earth in early August.

After detaching from the ISS, Crew Dragon will begin its descent, splashing down in the Atlantic Ocean off the coast of Florida.

It will be slowed down by four large parachutes, the same method used for the return of NASA's Apollo capsules, although they landed in the Pacific.