A man suspected of kidnapping his children at knifepoint led police on a high-speed chase and crashed into a tree, killing himself and two of the three children, authorities said.

The only survivor, the man's 17-year-old stepdaughter, was flown to a Sioux Falls hospital 45 miles from the crash site.

Angela Mogck's injuries were not believed to be life-threatening, Capt. Kevin Joffer of the Highway Patrol said Friday. Lyle E. Doering, 42, of Mitchell, and his children Deanna Mogck, 13, and Trevor Doering, 9, died in the crash.

The chase started after an alert went out about children being abducted at knifepoint from their grandmother's home in Ethan about 6:30 p.m., Joffer said.

Doering tied up the children's grandmother and took the children in her vehicle, the South Dakota Attorney General's Office said late Friday afternoon. The grandmother was able to get free and called 911.

He said a Hanson County deputy was chasing the vehicle and a Highway Patrol trooper put out spike strips on a rural road near Bridgewater to deflate the tires. Doering went into a ditch to avoid the spike strips, Joffer said, and some time later, the minivan hit the tree and caught fire.

"I don't know if it (crash) was deliberate or not," Joffer said.

State authorities are investigating. Hanson County Sheriff Mark Kessler said the unidentified deputy who pursued the van followed department policy.

An indictment returned May 21 in Lincoln County charged Doering with one count of sexual contact with a child, a 9-year-old who was not in the car, prosecutor Tom Wollman said.

A fugitive task force had been looking for Doering since the indictment, but the document was sealed and it was unclear whether Doering knew about it, Wollman said.

"He clearly presented a threat to these children. If those officers had called me looking for advice, I would have unequivocally told them to continue to pursue him," Wollman said.