"When the wreckage is dispersed like that, it indicates the likelihood of inflight breakup," National Transportation Safety Board Acting Chairman Christopher A Hart said late last night.
Learning where aircraft parts fell will help investigators determine when and how the breakup occurred, he said.
The crash almost certainly dashed founder Richard Branson's goal of starting commercial suborbital flight next spring, but the mogul said that while he remained committed to civilian space travel "we are not going to push on blindly."
"We are determined to find out what went wrong," he said, asserting that safety has always been the top priority of the programme that envisions taking wealthy tourists six at a time to the edge of space for a brief experience of weightlessness and a view of Earth below.
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"Yesterday, we fell short," he said. "We'll now comprehensively assess the results of the crash and are determined to learn from this and move forward."
The pilot killed in the test flight was identified Saturday as Michael Tyner Alsbury, 39, of nearby Tehachapi. The surviving pilot is Peter Siebold, 43, who parachuted to safety and was hospitalised.
Both worked for Scaled Composites, the company developing the spaceship for Virgin Galactic. Scaled Composite said Alsbury was the co-pilot for the test flight. Siebold, who was piloting SpaceShipTwo, "is alert and talking with his family and doctors," the company said in a statement.
More than a dozen investigators in a range of specialties were forming teams to examine the crash site, collect data and interview witnesses, Hart said.
"This will be the first time we have been in the lead of a space launch (accident) that involved persons onboard," said Hart, noting that the NTSB did participate in investigations of the Challenger and Columbia space shuttle disasters.
Hart said he did not immediately know the answers to such questions as whether the spaceship had flight recorders or the altitude of the accident, but noted that test flights are usually well-documented. Investigators will review video from multiple cameras that were on the spaceship, the mother ship, at nearby Edwards Air Force Base and a chase aircraft, he said.
Virgin Galactic, owned by Branson's Virgin Group and Aabar Investments PJS of Abu Dhabi, plans to fly passengers to altitudes more than 62 miles above Earth. The company sells seats on each prospective journey for USD 250,000.
The company says that "future astronauts," as it calls customers, include Stephen Hawking, Justin Bieber, Ashton Kutcher and Russell Brand. The company reports receiving USD 90 million from about 700 prospective passengers.