Two NASA astronauts have entered the International Space Station (ISS) after a landmark 19-hour journey on SpaceX, the first crewed US spacecraft since 2011.

The private enterprise is owned by billionaire entrepreneur Elon Musk.

Nasa astronauts Doug Hurley and Bob Behnken set foot on the ISS more than two hours after docking with the orbiting laboratory.

The pair had to wait for pressure and leak checks to be completed before exiting the Crew Dragon capsule.

They were greeted by fellow American Chris Cassidy as well as two other space station residents, Russia cosmonauts Anatoli Ivanishin and Ivan Vagner, as they made their way out of their spacecraft.

Both are now officially members of the Expedition 63 crew.

Mr Hurley and Mr Behnken began their 19-hour journey on SpaceX's Dragon capsule on top of the Falcon 9 rocket from Cape Canaveral in Florida on Saturday evening.

Although the space station orbits at around 350km above the planet, it took almost a day for the Dragon to rendezvous with the moving laboratory.

The spacecraft had to perform a series of manoeuvres to raise its orbit to come close enough to dock at the space station.

The Dragon docked autonomously to a port on the bow section of the station's Harmony module at 3.16pm Irish time, 16 minutes ahead of schedule.

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Mr Hurley congratulated the teams at Nasa and SpaceX, saying: "It's been a real honour to be just a small part of this nine-year endeavour since the last time a United States spaceship has docked with the International Space Station."

Shortly after the bell rang on the space station to mark the arrival of the Crew Dragon capsule, Mr Cassidy said: "Dragon arriving.

"The crew of Expedition 63 is honoured to welcome the Dragon and the Commercial Crew Programme."
He added: "Bob and Doug, glad to have you as part of the crew."

The mission, named Demo-2, marks the first time NASA has launched astronauts from US soil in nine years.

SpaceX also made history by becoming the first private company to send humans into orbit. The aim of the mission is to demonstrate SpaceX's ability to ferry astronauts to the space station and back safely.

NASA astronauts Doug Hurley (R) and Bob Behnken (2R) join NASA astronaut Chris Cassidy (C) and Russian cosmonauts, Anatoly Ivanishin (L) and Ivan Vagner (2L) aboard the International Space Station

It is the final major step required by SpaceX's astronaut carrier, the Crew Dragon, to get certified by NASA's Commercial Crew Programme for long-term manned missions to space.

The mission is expected to last anything between one and four months, with a number of tests being performed on the Dragon. 

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

The two-stage SpaceX rocket blasted off smoothly in a cloud of orange flames and smoke from Launch Pad 39A for the 19-hour voyage to the ISS.

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