BLUE HILL, Neb. (AP) — A school bus and a tractor-trailer collided in rural southern Nebraska, killing two children and two drivers, the Webster County Sheriff ’s office said Thursday.

At least four more children were transported to hospitals after the fiery crash at a rural intersection near Blue Hill around 5 p.m. Wednesday, sheriff ’s officials said.

The driver of the truck, 21- year-old Travis Witte, was hauling bales of hay for the family farm when the fatal crash occurred, his mother said.

“He had a big heart,” said Penny Witte, of Blue Hill. She said authorities have given her no details about the crash.

Four children, aged 6 to 10 years, were taken to Mary Lanning Memorial Hospital in Hastings, 20 miles north of Blue Hill, according to the Lincoln Journal Star.

A 7-year-old girl was later transferred to Children’s Hospital & Medical Center in Omaha and was in serious condition Thursday morning, hospital spokeswoman Cherie Lytle said.

One child was treated then released from Mary Lanning Memorial on Wednesday, while a girl underwent surgery and was in stable condition Thursday, hospital spokeswoman Lisa Brandt said. A boy remained at the hospital Thursday in stable condition, Brandt said. She did not have their ages.

The sheriff ’s office referred further questions about the crash to Webster County Attorney Sara Bockstadter, who did not return messages Thursday morning.

The bus was carrying students from the Blue Hill Community Schools, which serves kindergarten through 12thgrade students.

Nebraska State Patrol spokeswoman Deb Collins said the truck was hauling hay, but had no details about the accident or the injured children. She also referred questions to Bockstadter.