BOISE, Idaho (AP) — A school bus rear-ended another as it was picking up kids on a rural eastern Idaho highway Monday morning, sending four students and both drivers to the hospital, authorities said.

One child had to be flown by air ambulance to Utah for treatment, the Idaho State Police said in a statement. Seventeen students were aboard the two buses at the time, while a few kids waiting to get on the bus escaped unharmed, police said.

The crash remains under investigation. The second bus was traveling “at a considerable amount of speed” at about 7:15 a.m., Idaho State Police Sergeant Benjamin Foster said, and the sun wasn’t yet up. “It was in that twilight-dawn period,” he said

The three students who were treated at a nearby hospital all appeared to have non-life-threatening injuries like broken noses, Foster said. Idaho state police said it wouldn’t release updates on the medical condition of the juvenile patients.

A photo from the crash released by state police showed a damaged bus on the side of the road, its front crumpled in and engine compartment exposed, with a few red warning lights still illuminated.

The collision happened on state Highway 25 near the small farming town of Paul, about 155 miles (250 kilometers) southeast of Boise and roughly the same distance northwest of Salt Lake City, Utah.

The Minidoka County School District wrote on Facebook that the district is “cooperating fully with authorities as the incident is reviewed.”

“Student safety is always our top priority,” the district wrote.