A crash involving multiple vehicles on an Ohio interstate Tuesday, including a charter bus carrying students and chaperones headed to a school event, has left at least six people dead and 18 others injured.

The chain reaction crash occurred at 8:52 a.m. local time Tuesday, according to the Ohio State Highway Patrol, on the westbound lane of Interstate 70. At least three of the vehicles caught fire as a result of the crash.

The crash occurred on the westbound lane of I-70 in Licking County, which is about 40 miles east of Columbus, Ohio's capital city, where the charter bus was headed.

Here's what to know about the crash.

What happened in the crash?

The exact cause of the crash has not yet been identified, but a charter bus and a semi truck both traveling west on I-70 crashed Tuesday morning about a half-mile before the Route 310 Etna interchange.

The National Transportation Safety Board said Tuesday it will be conducting an investigation into the crash, and investigators plan to be at the crash site Wednesday to begin a preliminary investigation that will produce a report in about 10 days.

According to investigators, the full, in-depth report from the crash won't be completed for another 12-18 months.

Dozens of emergency personnel were dispatched to the crash just after 9 a.m. Tuesday, and area hospitals had been placed on alert for a "mass casualty incident, level 3," indicating that 10 or more people had been injured, and there was a need for paramedics, fire crews and hospital readiness across the region.

What vehicles were involved in the crash?

The crash involved five vehicles total, Ohio State Highway Patrol Lt. Nate Dennis said, including a charter bus, a tractor-trailer, another commercial vehicle and two passenger vehicles.

Where was the charter bus headed?

The charter bus carrying students and chaperones was headed to the last day of the Ohio School Boards Association conference in Columbus. It was occupied by a driver and 54 students, teachers and chaperones from Tuscarawas Valley Local Schools in Zoarville, Ohio.

Who were the victims?

Three students on the bus were killed: John W. Mosely, 18, and Katelyn N. Owens, 15, both of Mineral City; and Jeffery D. Worrell, 18, of Bolivar, according to the Ohio Highway Patrol Granville Post.

A teacher and two other chaperones died after accompanying the students in one of the two passenger vehicles involved in the crash. They are: Dave Kennat, 56, of Navarre; Kristy Gaynor, 39, of Zoar; and Shannon Wigfield, 45, of Bolivar.

Conference canceled

In the wake of the crash, the Ohio School Boards Association announced they canceled the last day of the annual convention.

"Given this devastating news, we have canceled (the remainder of) our conference," an association statement read. "Right now, our focus is on providing support to Tuscarawas Valley. That includes making grief counselors from our trade show available."

What are officials and politicians saying about the Ohio crash?

Ohio Gov. Mike DeWine spoke to media Tuesday at a rest stop on I-70, and said his prayers went out to everyone involved in the crash and their families. He ordered flags be flown at half-staff in Tuscarawas County, where the school students were from, and at the Statehouse in Columbus, in memory of the victims.

“This is our worst nightmare when we have a bus full of children involved in a crash and certainly the worst nightmare families can endure or a school can endure, DeWine said.

On Tuesday night, Tuscarawas Valley Superintendent Derek Varansky said school will be in session Wednesday, "but it will not be a normal day.”

A vigil was held Tuesday night at the Tuscarawas Valley High School football field, where some students involved in the crash were present.

Contributing: Bethany Bruner and Cole Behrens, Columbus Dispatch; Associated Press