The accident happened about 2 1/2 minutes into the flight from Cape Canaveral, Florida. A billowing white cloud emerged in the sky, growing bigger and bigger, then fiery plumes shot out of where the rocket was supposed to be, and pieces could be seen falling into the Atlantic. More than 5,200 pounds (2,360 kilograms) of space station cargo were on board, including the first docking port designed for future commercial crew capsules.
"We appear to have had a launch vehicle failure," announced NASA commentator George Diller. Data stopped flowing from the Falcon 9 rocket around 2 minutes and 19 seconds, he said. No astronauts were on board.
The rocket shattered while traveling at 2,900 mph (4,670 kph), about 27 miles (43 kilometers) up. Everything appeared to go well in the flight until the rocket went supersonic.
SpaceX founder and chief executive Elon Musk later said an over pressurization occurred in the liquid-oxygen tank of the rocket's upper stage.
"That's all we can say with confidence right now," Musk said via Twitter. "Will have more to say following a thorough fault tree analysis."
SpaceX President Gwynne Shotwell assured reporters, at an early afternoon news conference, that the company will fix the problem -- "and get back to flight."
She declined to speculate on what it would take to resume launches. She said the company had followed all procedures with respect to safety.
Losing this shipment -- which included replacements for items lost in two previous failed supply flights -- was a huge setback for NASA in more than one way. The space agency is counting on private industry to transport cargo -- and eventually astronauts -- to the orbiting lab. The California-based SpaceX is one of the contenders.
"This is a tough day," said NASA's top spaceflight official, William Gerstenmaier. He said there was nothing common among the three accidents, "other than it's space and it's difficult to go fly."
This is the second failed station shipment in a row and the third in eight months.
In April, a Russian cargo ship spun out of control and burned up upon re-entry, along with all its precious contents. And last October, an Orbital Sciences Corp. supply ship was destroyed in a launch accident.
This Dragon had been carrying replacement food, clothes and science experiments for items lost in those two mishaps. The seven previous SpaceX supply runs, dating back to 2012, had gone exceedingly well.
"This is a blow to us," Gerstenmaier told reporters, citing the docking port, a spacesuit and considerable research that had been on board. The space agency expected losses, just not three in under a year, he said.
The three space station residents were watching the launch live from orbit, including astronaut Scott Kelly.
"Sadly failed," Kelly said via Twitter. "Space is hard."
NASA Administrator Charles Bolden and other officials stressed that the space station crew is in no immediate trouble because of this latest loss. Late last week, NASA's space station program manager, Mike Suffredini, said the outpost had enough supplies on board to make it to October or so.
Russia expects to take another crack at launching supplies on Friday from Kazakhstan. And the Japanese Space Agency is on track to send up supplies in August.
But it wasn't immediately clear whether Russia's plans to launch three more men on July 22 would stay on track. Retired Canadian astronaut Chris Hadfield -- a former station commander -- said the supply situation could prompt another delay in sending up the crew. The Soyuz mishap in April already has delayed the trip by two months.
"You don't want to launch another crew if there's not going to be enough food, enough water," Hadfield said in an online chat. But Gerstenmaier said the crew flight would go on as planned.
SpaceX is one of two private companies hired by NASA to start ferrying American astronauts to the space station as early as 2017. The other contender is Boeing.
Shotwell said the first stage of the rocket seemed to work well. The company had hoped to land the discarded booster on an ocean platform.
Kelly's identical twin, Mark, a former space shuttle commander who is taking part in medical studies on the ground, pointed out that SpaceX, until now, had "a great record" with its Falcon 9 rockets. "These things happen," he said in a tweet. "They will figure this out." He spoke to his brother and reported, "He's paying close attention" to the situation involving the catastrophic failure.
Sunday, by the way, was Musk's 44th birthday. The SpaceX's billionaire founder also runs his electric car company, Tesla.