One person was in custody, Austin police said.
School officials tweeted that there is “no additional immediate threat to campus,” KPRC-TV reported.
However, police were warning people to avoid the area.
Student Rachel Prichett told the AP she was standing in line at a food truck outside the gym when she saw a man with a knife that resembled a machete approach the person standing behind her.
“The guy was standing next to me,” she said. “He grabbed him by the shoulder and shoved the knife in it. I just started running as fast as I could.”
Another witness, Ray Arredondo, 22, said he was walking to his car when a mass of students near the gym started running.
“They were just screaming, ‘Run! Get out of here!'” Arredondo said.
He later saw what looked like CPR being performed on someone outside the front door of the gym. Another student, Arredondo said, was sitting on a bench being treated for cuts to the head or neck.