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Witnesses reported seeing a fireball, hearing multiple explosions, feeling shock waves in buildings several miles away at Kennedy Space Center and seeing a plume of smoke rising from Launch Complex 40 just after 9 a.m.
“SpaceX can confirm that in preparation for today's static fire, there was an anomaly on the pad resulting in the loss of the vehicle and its payload," SpaceX said in a statement. "Per standard procedure, the pad was clear and there were no injuries.”
SpaceX CEO Elon Musk said that a failure occurred while the rocket was being fueled for a test-firing of its main engines, part of preparations for a planned early Saturday launch of a commercial communications satellite in which Facebook had a stake.
"Originated around upper stage oxygen tank," Musk said on Twitter. "Cause still unknown."
Facebook had planned to use some of the satellite's capacity to expand its Internet.org initiative in Africa.
"I'm deeply disappointed to hear that SpaceX's launch failure destroyed our satellite that would have provided connectivity to so many entrepreneurs and everyone else across the continent," Mark Zuckerberg said in a post on his Facebook page. Zuckerberg was in Africa promoting the satellite's benefits ahead of the upcoming launch. "We remain committed to our mission of connecting everyone."
Facebook had partnered with French company Eutelsat, which also planned to use the Amos-6 satellite to expand broadband Internet access in sub-Saharan Africa.
WATCH: SpaceX explosion
The so-called "static fire" test is a standard pre-launch milestone that SpaceX performs. It serves as a countdown rehearsal that fuels the rocket and is intended to culminate in a brief firing of the rocket's nine Merlin main engines, while the rocket remains held down on the pad.
The pad at Launch Complex 40 was cleared of personnel for the hazardous operation.
The accident comes just more than a year after SpaceX suffered its only in-flight failure by a Falcon 9, about two minutes into a launch of International Space Station supplies for NASA.
That failure was attributed to a broken strut that caused the upper-stage oxidizer tank to rupture, resulting in the rocket breaking apart.
SpaceX returned the Falcon 9 to flight six months later, and had completed nine successful launches since December, including eight by an upgraded, more powerful version of the rocket.
The company has made headlines during that period for landing six Falcon boosters, part of Musk's effort to develop reusable rockets.
In addition to an investigation into any problems with the rocket, it was not immediately clear whether the launch pad suffered significant damage.
The accident also came a year before SpaceX hoped to launch a first test flight with astronauts to the International Space Station as part of NASA's Commercial Crew Program.
Boeing is competing with SpaceX to fly the first crew. Boeing plans to fly its CST-1000 Starliner capsule on United Launch Alliance's Atlas V rocket, which has not suffered a major failure in more than 60 missions.
Kennedy Space Center's Emergency Operations Center personnel were monitoring the situation and standing by to assist if required, while the environmental health office monitored air quality to ensure it is safe for employees, said spokesman Mike Curie.
In a statement, U.S. Sen. Bill Nelson, D-Fla., said the accident was a reminder that spaceflight is risky.
“As we continue to push the frontiers of space, there will be both triumphs and setbacks," he said. "But at the end of the day, I’m confident that our commercial space industry will be very successful.”
SpaceX's eight successful launches this year were its most in any calendar year, and the company hoped to complete as many more before the end of the year. The upcoming missions potentially included the debut of a heavy-life Falcon rocket from a different launch pad at Kennedy Space Center.
The explosion startled the staff at the Titusville (Fla.) Area Chamber of Commerce.
“We were sitting here and all of a sudden it sounded like a sonic boom and the building started to shake,” said Denny Waktins of the chamber. “There were a couple of minor booms after that and then we went outside and saw the smoke plume. It was a well-defined plume, not like a controlled burn.”