The Boeing Starliner lifted off on an United Launch Alliance's (ULA) Atlas V rocket from the Cape Canaveral Space Force Station in Florida after multiple delays.

"This Crew Flight Test aims to certify the spacecraft for routine space travel to and from the International Space Station," NASA said.

The 58-year-old Williams is the pilot for the test flight while Wilmore, 61, is the commander of the mission.

The launch of this 25-hour flight to the ISS marks the beginning of the NASA-Boeing Starliner Crew Flight Test (CFT), Boeing said.

"This crew flight test represents the beginning of a new era of space exploration as we watch astronauts Wilmore and Williams put Boeing's Starliner through its paces on the way to the International Space Station," said Ted Colbert, CEO of Boeing Defense, Space & Security President.

"This is a great start. We look forward to getting the astronauts safely to the space station and back home," Colbert said in a press release.

Along with the two crew members, Starliner is also carrying about 760 pounds (345 kgs) of cargo.

Once docked to the Space Station, Williams and Wilmore will spend about a week there before returning to Earth. Following a successful Crew Flight Test (CFT), Boeing and NASA will continue working to certify Starliner for long-duration operational missions to the ISS.

Boeing's Crew Flight Test has been delayed multiple times given the setbacks in the spacecraft's development. The Starliner was "scrubbed off" just three minutes and fifty-one seconds before lift off on Sunday, June 2, due to "an observation of a ground launch sequencer", NASA said.

"The system was unsuccessful in verifying the sequencer’s necessary redundancy," NASA added.

Earlier in May as well, Starliner spacecraft was postponed after a valve glitch was discovered in the upper stage of the rocket intended to propel into space.

With its launch finally, Boeing became the second private firm to be able to provide round-trip crew transport to the International Space Station, other than Elon Musk's Space X.

Notably, Williams scripted history by being the first woman to embark on such a mission to space and it certainly won't be her first entry in the history books.

During a prior trip to the ISS in 2012, Williams had become the first person to finish a space triathlon. She had simulated swimming using a weight-lifting machine and ran on a treadmill while being strapped in by a harness so she wouldn't float away.

Sunita Williams was selected by NASA as an astronaut in 1998 and she is a veteran of two space missions -- Expeditions 14/15 in 2006 and 32/33 and 2022.

She served as a flight engineer on Expedition 32 and then commander of Expedition 33.

(With agency inputs)