Westland Milk Products issued a notice after a pipe burst at their Hokitika factory on Sunday afternoon.
Anyone on the Hokitika riverbank cycleway between 1pm and 4.30pm is being advised to seek medical attention in case they have come into contact with a potentially harmful liquid.
Communications Manager Steve Attwood said anyone who came into contact with the liquid vapour might experience skin rashes, sore or damaged eyes or have respiratory irritation if the vapour was inhaled.
People who were on the cycleway behind the factory and believe they have been in contact with the vapour should see their own doctor, local hospital A&E or call the chemical hotline on O800 243 622 for advice. They should explain they might have been in contact with “ACIDBLEND N600” in dilute form.

The accidental releasing the across the walkway of the liquid occurred between 1pm and 3pm approximately but, as a precaution, anyone in the area up to 4.30pm should get medical advice.
“Even if someone who came in contact with the spray is not showing symptoms, they are best advised to seek medical advice,” Attwood said.
Attwood said Westland notified the Grey Base Hospital accident and emergency department and Hokitika medical centres.
Westland also notified WorkSafe, local authorities and launched an internal investigation into what happened and how, with a view to ensuring it did not happen again, he said.