Two US astronauts have kicked off a new era of human space flight with an historic first: a launch into space from US soil using a rocket built in the US by a private company.

Astronauts Doug Hurly and Bob Behnken rumbled upwards, entering orbit 12 minutes into flight, signalling the end of the climb into space.

The nail-biting launch successfully skirted volatile weather conditions that had already delayed take off from Wednesday, the planned date.

“It’s been way too long,” NASA’s Jim Bridenstine said following the launch. “I was praying, I’m not going to lie to you.”

Live webcast of Crew Dragon’s test flight with @NASA astronauts @AstroBehnken and @Astro_Doug → https://t.co/bJFjLCzWdK https://t.co/qalF7oCJO6

— SpaceX (@SpaceX) May 30, 2020

The astronauts took off in the Dragon capsule on a Falcon 9 rocket, both built by private commercial spaceflight company SpaceX.

The astronauts on the Demo-2 mission are to head to the International Space Station (ISS).

It was the first launch from US territory in nearly a decade and the first time a private firm, rather than a government space agency, has sent astronauts into orbit.

If everything goes according to plan, the two astronauts will dock at the ISS on Sunday, where they will likely remain for months.

Astronauts Doug Hurley and Bob Behnken getting ready for orbit.

The purpose of the trip is to complete the validation of human spaceflight operations for SpaceX hardware, which will pave the way for private companies to ferry astronauts to the ISS.

According to NASA, SpaceX, along with Boeing, which is also developing rockets, will be able to launch crews to low-earth orbit allowing the government agency to focus on deep space missions – with an eye towards Mars.

Since the US stopped its own launches in 2011 under then-president Barack Obama to focus on deep space missions, the country’s space program has relied on hitching rides aboard Russian Soyuz rockets, at a growing cost.

SpaceX founder Elon Musk celebrates after the successful launch of the Falcon 9 rocket. Photo: Getty

On Wednesday, Hurley and Behnken were aboard the capsule, preparing to blast off from the space centre in Florida when they were informed that the launch was scrubbed, just minutes before the much-anticipated take off.

SpaceX, the Elon Musk-founded company which built the rocket and capsule, has a history of cargo launches to the ISS.

The company’s vessels have reached the station about 20 times with supplies, including scientific gear. However, this will be its first human cargo.

US President Donald Trump speaks near a SpaceX Crew Dragon capsule after the launch. Photo: Getty

Earlier

Elon Musk’s private rocket company SpaceX is set for a second attempt at launching two Americans into orbit from Florida for a mission that would mark the first spaceflight of NASA astronauts from US soil in nine years.

The mission’s first attempt on Wednesday was called off with less than 17 minutes remaining on the countdown clock due to stormy weather around the Kennedy Space Center at Cape Canaveral.

With forecast weather conditions likewise precarious, mission managers plan to make an earlier decision in a bid to avoid unnecessarily wearing out the crew with another suit-up and full day of launch preparations.

Elon Musk is behind the first privately owned manned mission. Photo: Getty

The launch is scheduled for around 5am (AEST).

“Back-to-back wet dress rehearsals” disrupt the astronauts’ sleep cycles, NASA chief Jim Bridenstine told a Friday news conference.

Barring weather or other unforeseen problems, the 24-storey SpaceX Falcon 9 rocket is due to lift off at 5.22am AEDT on Sunday, propelling astronauts Doug Hurley and Bob Behnken aloft on a 19-hour ride to the International Space Station.

They will be carried there inside the newly-designed Crew Dragon capsule, making its first flight into orbit with humans aboard.

The launch pad is the same one used by NASA’s final space shuttle flight, piloted by Hurley, in 2011. Since then, NASA astronauts have had to hitch rides into orbit aboard Russia’s Soyuz spacecraft.

The last time NASA launched astronauts into space aboard a brand new vehicle was 40 years ago at the start of the shuttle program.

President Donald Trump and Vice-President Mike Pence visited the Kennedy Space Center three days ago for the first launch attempt, with Trump saying he plans to return for the retry.

-AAP