WICHITA, Kansas (CNN) -- A grain elevator exploded Monday, killing two people and trapping four others under the wreckage, officials said.

At least six people were injured in the blast, one of them critically, emergency workers said.

Four men were trapped inside a tunnel under the three-quarter-mile-long elevator complex, said Ken Cox, division chief of the Sedgwick County Fire Department.

County Chairman Mark Schroder said there had been some communication with the trapped workers, but that the communication had stopped.

Rescue workers did not immediately try to reach the four men while crews worked to determine if the building was structurally sound.

Army helicopters from Fort Riley, Kansas, and a 300-foot crane were used to rescue six workers from the roof of DeBruce Grain Elevator in southwest Sedgwick County, south of Wichita. Four others were rescued from inside.

County spokesman Fred Ervin said the 9:20 a.m. explosion caused extensive damage in what is known as the north Headhouse, the tallest building in the elevator complex. He said workers were evacuated from the south end of the complex.

He said authorities believe the explosion may have been caused by a spark, but that has not been confirmed yet. Grain dust is extremely explosive.

The force of the blast could be felt in nearby residential areas.

related reading	book search