Incorrectly mixed pool chemicals have caused a chemical reaction and forced a 100 metre exclusion zone to be set up around a Northland high school.

A Kaipara home was evacuated as part of the zone around Ruawai College.

Fire services say incorrectly mixed pool chemicals caused the chlorine gas reaction on Wednesday morning.

Crews attended the scene and were able to isolate the chlorine and clear the area by 2pm.

One person was treated by paramedics after the incident for what is understood to be only minor injuries.