Staff at a school in Canterbury used the school's defibrillator to help one of their colleagues who collapsed this morning.

Geraldine High School deputy principal Jo Nicolson went into cardiac arrest about 8.30am.

Emergency services were quick to arrive at the school and took her to Timaru Hospital in a serious condition, but not before two staff members used a defibrillator to assist her.

Principal Simon Coleman was not yet available for comment, but the school posted a message about Mrs Nicolson's condition via their social media websites.

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"This morning Mrs Nicolson collapsed. We are pleased that Mr Rogers and Mr Brown were able to respond and help her. They did have to use the defibrillator."

Grant Rogers is another deputy principal and Drew Brown is the head of the outdoor education department.

Just after 1pm, Geraldine High staff posted an update on its official Facebook page.

"We have received an update from Mr Nicolson, Jo's husband, that she had a cardiac arrest, is in ICU and breathing on her own.

"Jo is receiving the best of care at Timaru Hospital and we are thinking of her, her family and friends at this time."

Today marked the first major NCEA exam for secondary school students. Up to 40,000 students sat level 1 mathematics around the country this morning.