Robert Sumwalt of the National Transportation Safety Board said they would be gathering evidence, including any mobile phone footage of the crash.
The balloon caught fire and plummeted to the ground in a field near Lockhart, about 30 miles (50km) south of Austin.
Witnesses have suggested it may have hit power lines.
The local sheriff's office said identification of those killed would be "a long process".
Neither the victims nor the operator of the balloon have been officially identified but friends and relatives named the pilot as Skip Nichols who ran Heart of Texas Hot Air Balloon Rides.
Wendy Bartch, a former girlfriend, said he had been involved with hot air balloons for about two decades.
"He was a good pilot and loved people," she told the Austin American-Statesman newspaper.
The Facebook page of the balloon ride company was filled with messages of condolence and pictures of Mr Nichols.
National Transportation Safety Board (NTSB) member Robert Sumwalt told reporters that the firm's records as well as photographs and videos taken by passengers and by people on the ground would be part of the investigation.
He said they would look at "the operation of the balloon, the pilot, [and] the company that operated the balloon".
Two years ago the NTSB called for better regulation of hot air balloon flights in the US, recommending they should be subject to the same oversight as tour planes and helicopters.
The FBI and the Federal Aviation Administration are also assisting in the inquiry.
Saturday's accident was the deadliest ever hot air balloon crash in the US.
US safety officials have arrived in Texas to investigate Saturday's crash of a hot air balloon in which all 16 people on board were killed.