16 people have died after a hot air balloon crashed in flames in central Texas in the worst such disaster in US history.
Authorities said identifying the victims will be "a long process" after the incident near Lockhart, around 30 miles south of Austin.
Although the US National Transportation Safety Board (NTSB) did not identify the company operating the balloon or its pilot, the flight is believed to have been run by Heart of Texas Hot Air Balloon Rides, while the pilot was named in reports as Skip Nichols, 49.
The balloon fell in pasture land close to a row of high-tension power lines.
Aerial photos showed an area of scorched land underneath, while one witness described seeing a "fireball" near the lines.
There are not thought to have been any children involved in the tragedy.
Alan Lirette, a colleague of the man named as the balloon's pilot, said: "That's the only thing I want to talk about, is that he's a great pilot.
"There's going to be all kinds of reports out in the press and I want a positive image there, too."
Wendy Bartch, a former girlfriend of Nichols, told the Austin American-Statesman that Mr Nichols was "a good pilot and loved people", was cautious about keeping passengers safe, and had been involved with hot air balloons for about two decades.
Mr Nichols' Facebook page identifies himself as the chief pilot of Heart of Texas. The operation does not appear to be registered with the state of Texas.
Heart of Texas' website said it offers rides in the San Antonio, Houston and Austin areas. The company's Facebook page features photos of a hot air balloon in the air, people waving from a large basket on the ground, and group selfies taken while aloft.
NTSB investigators will look at "three things - human, machine and environment," said board member Robert Sumwalt.
The investigation will include inquiries into the balloon's maintenance history and the weather conditions at the time of the crash.
Investigators will also look into whether the operator filed a passenger manifest before taking off.
The NTSB is interested in any footage of the flight shot by witnesses, while investigators will look for devices in the wreckage that might contain video evidence.
Margaret Wylie, who lives about a quarter of a mile from the crash site, described hearing a popping sound.
"I looked around and it was like a fireball going up," she said, noting that the flames were almost high enough to reach the power lines.
Warning about potential high-fatality accidents, safety investigators recommended two years ago that US Federal Aviation Administration (FAA) should impose greater oversight on commercial hot air balloon operators.
The FAA rejected those recommendations, which led to the NTSB classifying the response as "open-unacceptable".
FAA spokesman Lynn Lunsford said it is difficult to say whether the Texas crash will cause the agency to reconsider the NTSB's recommendations "until we've had a chance to gather and examine the evidence in this particular case".
Saturday's crash was one of the worst hot air balloon accidents on record. In 2013, 19 people were killed and two were injured when a balloon caught fire over Luxor, Egypt, and plunged 1,000ft.