Six students hospitalised after mystery substance released in prank gone wrong

Six students had to be hospitalised and dozens more evacuated from a block of classrooms in Adelaide after a prank went horribly wrong.

The teenagers were overcome by a substance let off by another student at Roma Mitchell Secondary College.

One by one, affected students were taken by ambulance to the Women's and Children's Hospital after inhaling a substance near a boy's toilet block on Monday afternoon.

"Heaps of people were coughing and their eyes were tearing up, and I didn't really know what happened," student Leyla Barnett said.

Dozens of students from nearby classrooms were evacuated as firefighters were called in to investigate.

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They had given the school the all-clear just minutes earlier, after they failed to confirm reports of a potential gas leak.

"You send your kids to school and hopefully they're safe," one parent said after the incident. "That's concerning."

Late on Monday afternoon the substance was confirmed as chilli spray, most commonly used in gardening.

The affected students have since been discharged from hospital, and one prankster classmate has some serious explaining to do.