A group of four Staten Island schools were temporarily evacuated Tuesday after they received calls of bomb threats, police said.

The schools -- Concord High School, Curtis High School, Ralph R. McKee Career & Technical High School, and Susan E. Wagner High School -- all received threats within minutes of each other around 11 a.m.

School officials and emergency personnel searched the schools and found nothing, police said. Students were all allowed back inside about 30 minutes later.

Police are investigating whether the same person called all four schools. It was not immediately clear why the threats were made or why the schools were targeted.