HAYSVILLE, Kan. (AP) _ An explosion rocked a grain elevator today, killing at least one person and seriously injuring at least three others.

The explosion happened about 9:20 a.m. in the north end of the Debruce Grain Elevator, the Sedgwick County Sheriff's Department said.

About six people were trapped on the roof of the grain elevator and helicopters were sent in to help them to safety.

About 20 other people were unaccounted for late this morning, but many may have just left the scene amid the confusion, said Fred Ervin, spokesman for the Sedgwick County Emergency Management Office. Damaged parts of the building were being searched to see if anyone was trapped, he said.

The explosion may have been started by a spark, Ervin said. Airborne grain dust is highly explosive.

``There's a lot of smoke. It seems like a large section of the roof is missing,'' Ervin said.

One person was in critical condition and two others were being treated for serious injuries at St. Joseph Medical Center, Ervin said.

Haysville is about five miles south of Wichita.