NASA's plans to begin launching astronauts from US soil this summer have suffered a major setback, after a SpaceX crew capsule burst into flames.
The aerospace company founded by billionaire entrepreneur Elon Musk was testing the Crew Dragon capsule's "SuperDraco" abort thrusters when the accident occurred.
The capsule was engulfed in smoke and flames but luckily the test area was clear, and no one was injured.
The capsule, which flew to the International Space Station (ISS) last month on a unmanned trial run, was supposed to be reused in a launch abort test in June.
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Another capsule was supposed to follow with two astronauts as early as July.
"This is why we test," NASA administrator Jim Bridenstine said in a statement.
"We will learn, make the necessary adjustments and safely move forward with our Commercial Crew Program."
NASA said it is too early to revise the target launch dates, given that the accident is still so fresh.
The abort thrusters, which are designed to fire in an emergency and pull the capsule safely away from the rocket, are crucial to protect astronauts in flight.
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Former NASA astronaut Garrett Reisman, who directed space operations for SpaceX until last year, said it was a "tough day ... not good" for the company.
"But thankfully no one got hurt and with everything we learn from this anomaly Crew Dragon will be a safer vehicle for all her future crews," he tweeted.
SpaceX said it will make sure, through the accident investigation, that the Dragon is one of the safest spacecraft built for astronauts.
NASA has not launched astronauts from Cape Canaveral since the last shuttle flight in 2011.
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It currently depends on Russian Soyuz rockets and spacecraft to get its astronauts to and from the ISS, at a cost of about $80 million (£60 million) per seat.
In 2014, the US space agency recruited two private companies - SpaceX and Boeing - to build new capsules to ferry astronauts to and from the space station.
SpaceX already works with NASA to transport food and equipment between Earth and the ISS, using its robotic Dragon cargo capsule.
However, there are a number of crucial differences between the Dragon cargo capsule and the Crew Dragon capsule .
As well as having seven seats, the Crew Dragon has a life-support system and a touch-screen console for astronauts to use.
It also features eight "SuperDraco" escape engines, which are designed to fly the capsule out of harm's way during a launch emergency.
Unlike the cargo capsule, which is grabbed by the space station's huge robotic arm as it flies past, Crew Dragon is designed to dock directly to the ISS .
NASA stressed that next week's launch of a SpaceX Dragon cargo capsule remains on track. The supply ship is set to blast off from Cape Canaveral on April 30.
