More than a dozen suburban Chicago high school students have received hospital treatment after a device was found in a hallway that may have contained toxic substances.

A spokeswoman for Joliet's Silver Cross Hospital, Tracy Simons, says 13 students from Lockport Township High School's Central Campus were brought in Monday morning. Ten have already been released. Simons says the three others are in good condition and could be released soon.

She declined to provide other details, including the nature of the injuries.

A school district statement says a plastic bottle was used to release black smoke and possible chemicals as students arrived at school.

The campus has been closed and all after-school activities canceled as police continue to investigate.