Lake Park High School's west campus in Roselle was evacuated Thursday because of a bomb threat, according to a message on the school website.
Students were moved to the adjacent Clauss Recreation Center and later taken home by bus while police secured the high school building at 500 W. Bryn Mawr Ave.
Officials said a "thorough sweep" determined the campus was safe for use but students will not be allowed to return to their classrooms until Friday.
There were no threats to the east campus, which remained in session, officials reported.
Neither school administrators nor Roselle police could immediately be reached for comment.
A message on the school website said some events at both the east and west campuses and off-campus locations are being canceled or relocated. For a list, visit www.lphs.org.