ROLLA, Mo. - Nearly two dozen people were being decontaminated Tuesday after a white, powdery substance was found on a man threatening "terrorist-type" actions at the University of Missouri-Rolla, school officials said.

"Possible bomb materials" were also found with the man, identified only as a student at the south-central Missouri university, school officials said in a statement.

The student was in custody and being questioned, the statement said.

Twenty-three people were sent through a decontamination process at the university's civil engineering building, where a police standoff with the student had started around 2:30 a.m.

The university was shut down during the standoff and classes for its 5,850 students were canceled. The school's primary focuses are engineering and technology.