A chemical spill resulted in 16 people being taken to hospital and the evacuation of a Hastings school yesterday.

Fire crews from Hastings and Napier were called to Camberley School in Hastings about 10am after reports of a chemical spill and a "toxic smell" in the school buildings.

By 11am students had gathered in the hall, and parents were told to collect their children as a "precautionary measure".

Principal Tamla Smith said the spill was believed to have come from an "old-fashioned" mercury thermometer in the science area, which broke on Friday afternoon.

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The broken thermometer parts had been cleaned up, but the mercury soaked into the carpet. With temperature hovering just under 30C this weekend, by the time the classrooms opened yesterday, it was believed the mercury had vaporised.

According to the Ministry of Health, a thermometer contains between 0.5 and 3g of mercury — less than a quarter of a teaspoon.

Liquid mercury is not readily absorbed through skin but vaporises at room temperature and inhaling the vapour can be harmful. Symptoms of exposure to the neurotoxin include tremors, insomnia, neuromuscular changes and headaches.

Smith said the school was advised to send students home in case the wind spread the toxicants.

For the rest of the afternoon, fire crews and a hazardous materials team decontaminated the affected classroom.

Fire Service assistant area commander Nigel Hall told Hawke's Bay Today when the students came back to school yesterday, the mercury had probably reacted with solvents in the carpet, and created fumes causing the teachers and pupils to feel unwell.

A number were taken to Hawke's Bay Hospital yesterday as a precaution. Some complained of respiratory problems.

Initially, Hall said seven students and two teachers were taken to hospital for observation.

This rose to nine, and by 2pm a Hawke's Bay District Health Board spokeswoman said 16 people had been checked by the hospital's emergency department — 13 children, two teachers and a parent.

No one was admitted.

Camberley School would be open today, Smith said, and the two affected classes would be housed in spare classrooms.

Yesterday fire crews removed the affected carpet and ventilated the classroom.

A Fire Service test yesterday afternoon showed no contaminants, but Smith said they would not be using the affected classroom until another clear test was received today.

She was unsure how much the incident might cost the school, although replacing all the carpet tiles would be covered by insurance. ​