Driver error is likely the cause of a crash involving a school bus and an empty freight train that killed two people and injured 12 more in northeastern North Dakota, police said Tuesday.

Evidence at the scene indicates the 62-year-old bus driver braked but didn't stop in time to prevent the crash Monday afternoon near Larimore, Highway Patrol Lt. Troy Hischer said. The bus driver and a 17-year-old girl were killed.

"There's no indication that the brakes didn't work properly. The driver was on the brakes -- you could see that he was trying to stop. We believe the brakes worked properly," Hischer said.

"We believe it was driver error at this point -- he became complacent, or something else was going on," he said.

Authorities were examining the bus for mechanical problems and planned to interview bus passengers to determine if the driver was distracted, Hischer said.

Hischer said the Larimore Public School District bus was heading north on a county road when it was struck by a westbound BNSF Railway freight train at a crossing with no crossing arms. He said the train struck the bus on the passenger side, near the doors. The bus driver and the 17-year-old student were ejected from the vehicle and killed.

Larimore is about 100 miles north of Fargo.

The ages of the students on the bus ranged from 5 to 17, Hischer said. Some of the injured suffered broken bones; three were in "very serious condition," he said.

Officials with Altru Health System in Grand Forks said Monday night that they had received 10 patients, six of whom were admitted and three of whom were transferred. One patient was released. The hospital did not immediately have an update early Tuesday.

Hischer said he has responded to numerous fatal crashes in his 21 years in law enforcement but was still shaken by Monday's incident.

"It's difficult," he said. "I have four children. It definitely hits home, when you see children (injured) like that."

Roger Abbe, superintendent of schools for the district, declined to comment Monday evening.

BNSF spokeswoman Amy McBeth said BNSF has sent investigators to the scene. McBeth said the train was not carrying any cargo and that neither of the two crew members on the train was injured.

U.S. Sen. John Hoeven from North Dakota sent his condolences.

"We pray for the speedy recovery of all who were injured, and that everyone involved finds solace in the love of their families and friends," Hoeven said in a statement.