Six helicopters airlifted the injured from the scene, taking them to 10 area hospitals, said Mack.
The bus was one of two that had been chartered to transport members of Channelview High School Falcon Band back to Houston, Texas, a spokesman for the Channelview Independent School District confirmed.
The district superintendent confirmed that 40 students and 6 adult staffers from the school were onboard the bus at the time of the crash, adding "We are now focused on getting everyone back safely to our community."
The second bus continued traveling to Houston and arrived outside the school at 1:30 p.m. (2:30 p.m. EST) local time. Family members rushed to hug students as they disembarked the bus, NBC Houston affiliate KPRC reported.
Houston-based First Class Tours confirmed it was the vehicle's operator.
"Our prayers are with the injured and their families at this time," the company said in a statement. "We pledge our assistance in cooperating with local authorities in the investigation."
U.S. Department of Transportation records show First Class Tours vehicles were involved in four crashes over the past two years — one of them fatal.
The National Transportation Safety Board dispatched a six-person team to investigate the incident.
A picture of the students outside Disney World in Orlando, Florida, had been posted as the cover photo on the band's Facebook page hours before the crash.
"I pray for a speedy recovery for all those injured, and I am especially grateful for the heroic actions of the Alabama first responders that undoubtedly helped save lives today," Texas Gov. Greg Abbott said.