A SpaceX Crew Dragon carrying four astronauts docked with the International Space Station overnight.

It is the first of what NASA hopes will be many routine missions ending US reliance on Russian rockets.

"Dragon SpaceX, soft capture confirmed," said an announcer as the capsule completed its 27-and-a-half hour journey at 4.01am (Irish time).

The second part of the procedure, known as "hard capture," occurred a few minutes later.

The spacecraft, named "Resilience," docked autonomously with the space station some 400km above the Midwestern US state of Ohio.

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The crew is comprised of three Americans - Michael Hopkins, Victor Glover and Shannon Walker - and Japan's Soichi Noguchi.

Earlier, mission commander Mr Hopkins gave pilot Mr Glover his "gold pin," a NASA tradition when an astronaut first crosses the 100km Karman line marking the official boundary of space.

Mr Glover is the first black astronaut to make an extended stay at the ISS, while Mr Noguchi is the first non-American to fly to orbit on a private spaceship.

The crew joins two Russians and one American aboard the station, and will stay for six months.

"Welcome to the ISS. We can't wait to have you onboard," said Kate Rubins, the US astronaut already on the space station.

Along the way, there was a problem with the cabin temperature control system, but it was quickly solved.

SpaceX briefly transmitted live images from inside the capsule showing the astronauts in their seats, something neither the Russians nor the Americans had done before.

The Crew Dragon capsule earlier this week became the first spacecraft to be certified by NASA since the Space Shuttle nearly 40 years ago.

Its launch vehicle is a reusable SpaceX Falcon 9 rocket. 

At the end of its missions, the Crew Dragon deploys parachutes and then splashes down in water, just as in the Apollo era.

SpaceX is scheduled to launch two more crewed flights for NASA in 2021, including one in the spring, and four cargo refueling missions over the next 15 months.

International Space Station (Pic: NASA)