The United States on Saturday launched a commercial spacecraft carrying two NASA astronauts, making it the first crewed flight to go into orbit from American soil since the final Space Shuttle mission in 2011.

After Wednesday's scrub due to unsuitable weather, the Crew Dragon space capsule, developed by U.S. aerospace manufacturer SpaceX, lifted off smoothly carried by a Falcon 9 rocket at 3:22 p.m. from NASA's Kennedy Space Center in Florida. It is expected to arrive at the International Space Station after a journey of about 19 hours.

The SpaceX Falcon 9 rocket with the manned Crew Dragon spacecraft attached takes off from launch pad at the Kennedy Space Center on May 30, 2020 in Cape Canaveral, Florida. (Getty/Kyodo)

With the SpaceX craft on course to become the first commercial spacecraft to carry humans to the ISS, the U.S. National Aeronautics and Space Administration has said the mission will lay the foundation for "a new era in human spaceflight" where space travel will become less expensive and available to more people.

The administration of President Donald Trump seeks to reassert U.S. leadership in space and refocus America's space program on human exploration, setting goals such as returning astronauts to the Moon and sending humans to Mars.

"A new age of American ambition has now begun. Past leaders put the United States at the mercy of foreign nations to send our astronauts into orbit. Not anymore," Trump said at the Kennedy Space Center.

"Today we once again proudly launched American astronauts on American rockets...from right here on American soil."

Undated file photo shows Japanese astronaut Soichi Noguchi, who will board Crew Dragon spacecraft, developed by U.S. aerospace manufacturer Space X and possibly to be launched within 2020. The 55-year-old stayed on the International Space Station for over 150 days from December 2009. (Kyodo)

Since NASA's costly Space Shuttle program ended in 2011 after 30 years of service, the United States has relied on Russian Soyuz spacecraft to transport its astronauts to the ISS.

In March of last year, the Crew Dragon succeeded in its first demonstration mission, an unmanned trip to and from the ISS. Saturday's second demonstration mission is SpaceX's final test flight to validate its crew transportation system, including the Crew Dragon, Falcon 9 and launch pad.

If the mission turns out to be a success, the crew for the next flight, possibly in late August, will include Japanese astronaut Soichi Noguchi, 55.

Under its Commercial Crew Program that started 10 years ago, NASA has worked with the private sector to develop a successor to the shuttle program, awarding SpaceX and Boeing Co. contracts worth $3.1 billion and $4.8 billion, respectively.

NASA reported earlier this month that the Commercial Crew Program is poised to save the agency approximately $20 billion to $30 billion and provide two independent crew transportation systems.

"Today's launch makes clear the commercial space industry is the future," Trump said, hailing U.S. billionaire entrepreneur Elon Musk for founding SpaceX in 2002 and making it the first private company to put humans into orbit around the Earth.

Artist's concept of Space X Crew Dragon(Image supplied by Space X)

Through live coverage provided by NASA, the two veteran American astronauts -- Douglas Hurley, 53, and Robert Behnken, 49 -- were seen ahead of liftoff wearing sleek white space suits while buckled up in front of touchscreen control panels inside the Crew Dragon capsule.

Technicians who helped the two prepare to board the capsule were wearing face coverings amid the coronavirus pandemic.

About 12 minutes after departure, the Crew Dragon separated from the Falcon 9 rocket's first and second stage boosters and continued its journey to the ISS.

The Crew Dragon will execute a series of burns, which will gradually raise its orbit to align more closely with the ISS before docking with it around 10:30 a.m. Sunday.

The ship is designed to dock autonomously, but the astronauts aboard will be ready to take control of the spacecraft if necessary, according to NASA and SpaceX, officially known as Space Exploration Technologies Corp.

Upon arriving at the ISS, Hurley and Behnken will conduct research and other tasks with the ISS crew, while running tests to ensure the Crew Dragon will be able to remain connected to the ISS for up to 210 days on future missions.

The Crew Dragon used for the current flight test can stay in orbit about 110 days, and the current mission's duration will be determined once it arrives at the ISS, according to NASA.

The Crew Dragon, with the two astronauts aboard, will depart the ISS and re-enter the Earth's atmosphere. It will splash down off the Atlantic coast of Florida, with the crew expected to be picked up at sea by SpaceX's recovery vessel.