A Fire and Emergency NZ (Fenz) spokesman said two fire appliances, a St John ambulance and a Dunedin City Council representative were called to Dunedin North Intermediate just before noon, after reports of a chemical spill.
School principal Heidi Hayward said a pupil was working on their science fair project when they dropped a mercury switch and broke it.
It caused a small amount of the toxic liquid metal to leak out on to the floor of the classroom.
A mercury switch is an electrical switch that opens and closes a circuit when a small amount of the liquid metal connects metal electrodes to close the circuit.
Exposure to mercury and mercury-containing organic compounds is toxic to the human nervous system, immune system and kidneys.
Ms Hayward praised the speed and efficiency of the emergency services response.
"As it turns out, the fire service deal with chemical spills, so no matter how small the mercury spill is, the fire service attends.
"But it’s great that they’re so proactive.
"It was awesome service in terms of being instant and really making sure that everybody was safe."
She said when there was a hazardous substance spill, Fenz automatically called St John in to check and treat anyone who may have come into contact with it.
"It’s just the student who dropped the mercury switch, and anyone who was sitting at the table with that student, [they] automatically get checked.
"No-one was treated for any injuries."
She said the only injury recorded was to the floor, where a carpet tile had to be removed and replaced to dispose of the spill.
