Two students at a San Jose middle school were taken to a hospital after they and others reported having difficulty breathing due to what was eventually determined to be elevated levels of carbon dioxide in a classroom this morning, fire officials said.

Crews responded shortly after 9am May 8 to Sunrise Middle School in the 1100 block of East Julian Street. They determined that most students' symptoms were resolving as of shortly before 10:30am and they could be released to parents or guardians, but two students were transported to the hospital for further evaluation.

The San Jose Fire Department's hazardous materials team responded and checked for airborne contaminants but all tests came back negative except for carbon dioxide. The department said on social media that the “source of CO2 has been removed and levels restored to normal” but did not identify the source of the carbon dioxide.

Classes resumed at the school and traffic had reopened as of 11am, fire officials said.