“It does not appear at this time that there were any survivors of the crash,” Caldwell County Sheriff Daniel Law said in a statement, according to his office.
The sheriff’s office said it was working to determine the identities of those aboard the balloon.
The Federal Aviation Administration confirmed the crash about 30 miles (50 km) south of Austin and did not offer any information on fatalities. The agency said at least 16 people were on board the balloon.
Texas Governor Greg Abbott offered his condolences to those killed in the crash.
“Our thoughts and prayers are with the victims and their families, as well as the Lockhart community,” he said in a statement.
More than a dozen police vehicles could be seen on pasture land at the site of the crash, in live video provided by Austin TV station KVUE.
The FAA said the crash took place at about 7:40 a.m. (1240 GMT) and the National Transportation Safety Board has been notified.
Lockhart is a town of about 13,000 people near state parks and home to a variety of barbecue restaurants considered to be among the best in the state.