Two children and one adult aide were killed when a bus veered across the median of a slick highway in Knoxville, Tenn. and struck another school bus full of children on Tuesday. Police said officials confirmed the death of Sunnyview Primary School students Zykia Burns, 6, and Seraya Glasper, 7. Kimberly Riddle, 46, also died at the scene. She was a youth minister and a teacher’s aide at Sunnyview according to Local 8 Now News.

A spokesman for the Knoxville police Darrell DeBusk explained that one bus flipped when the other made a sudden, unexplained sharp left turn, crossed over the median and crashed into the other bus on Asheville Highway and John Sevier Highway around 2:50 p.m. ET, according to NBC News. The crash took about eight hours to clear.

James Davenport, 47, was driving the Chilhowee Intermediate bus that crossed over the concrete median. Joe Gallman, 67, was driving the Knoxville bus transporting students from Sunnyview Primary School.

Davenport was among eight other patients who were transported to University of Tennessee Medical Center. WBIR reported that six have been released. Davenport was not treated for any life-threatening injuries. Two children and one adult were also reported stable.

Knox News said that 20 students were taken to East Tennessee Children’s Hospital. Eighteen were taken by KAT bus and two by private transportation according to hospital officials. Emergency room director Dr. Ryan Redman said the children were treated for injuries such as scrapes, bumps, bruises and cuts. All 20 children were released on Tuesday night. Students who were not injured in the crash reunited with loved ones at the scene.

Jim McIntyre, Knox County Schools Superintendent, said the crash was an “unspeakable tragedy” at a news conference in Knoxville. He referred to the victims of the crash as some of the youngest members of the Knox schools family and ensured the community that they work to prevent such happenings every day.

Knoxville Police Chief David Rausch also called the event a “tragedy” and expressed his grief for the families involved. He asked for prayers for the loss of lives from the community as he held back tears.

Sunnyview Primary School and Chilhowee Intermediate School cancelled classes on Wednesday and provided on-hand grief counselors for students or anyone in association with the accident in need of support from 10 a.m. to 2 p.m. The children range from kindergarten to third grade at Sunnyview and Chilhowee Intermediate.

Authorities are still searching for what may have caused the fatal collision that left three dead and 27 with minor injuries or in the hospital, according to Knox News. Authorities did point out that there was sporadic rain throughout the day. They also noted that school buses in Tennessee do not require seat belts.

Both buses involved in the crash passed inspections in the fall with no major problems reported, according to the Tennessee Department of Safety. Both buses were also less than 15 years old.  Robinson also said that bus drivers have to go through training each year with the Department of Public Safety.

Officials say they will continue to interview people about what happened. The National Transportation Safety Board will be assisting in the investigation.