ELMWOOD PARK, N.J. (CBSNewYork) — Students at an elementary school in Bergen County, New Jersey were tested for carbon monoxide poisoning after three of their classmates became sick Wednesday afternoon.

It happened at Gantner Avenue Elementary School around 1:30, when the fire department says at least two children fainted and other children complained of stomach pains and nausea.

The entire school was evacuated.

One parent just happened to be at the school when she saw first responders arrive.

“I just came to pick up my child,” the frantic mother told CBS2’s Valerie Castro. “The whole school was closed. There was police officers, there were firefighters. They say there were carbon monoxide, um, leak or something like that, and they were testing the kids to see if they’re fine. Everything seems to be okay but I’m still nervous.”

In addition to the three students, a custodian and a firefighter were taken to a local hospital for evaluation.

Authorities say the CO came from a leak in the school’s heating system.

The school has been deemed safe by authorities and school will reopen Thursday, according to Elmwood Park Schools Superintendent Anthony Grieco.

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