Four people were injured in a fire at the Austin City Limits Music Festival in Zilker Park.

It is believed a propane tank near a camper for staff members exploded around 2:30 Friday afternoon, and the flames spread to a food trailer in a beverage area.

EMS officials say four people were burned, two with life-threatening injuries. All four were taken to Brackenridge Hospital. The two critically injured patients were later flown to the burn unit at the Brooke Army Medical Center in San Antonio.

Thick black smoke billowed hundreds of feet into the air and could be seen for miles from the park.

No word yet on what caused the fire.

The music continued on all the stages, and officials say the general public was never in danger.

KVUE meteorologist Mark Murray was on the scene and says that the public didn't panic.

"It was very calm, very orderly. In fact, people continued to come into the park," said Murray. "A small area near the fire was roped off."

Mark Murray / KVUE News

Four people were injured in a fire at the ACL Festival.

Tens of thousands of music fans are expected to attend the ACL Festival this weekend as 130 bands perform on eight stages in Zilker Park.