Two people were taken to Causeway hospital by ambulance after a leak at a dairy processing facility.
The PSNI said Creamery Road and Ballylagan Road to the east of Coleraine have been closed to traffic due to the incident at Ballyrashane Creamery.
They had reopened at about 1pm.
Six fire engines were at the scene, where an ammonia spill was reported during the morning.
The fire brigade said: “Firefighters have isolated a leak at the premises and there is no immediate risk to life or property. The premises has been evacuated and all persons inside the property have been accounted for.”
The Ambulance Service said the pair who were taken to hospital had been “suffering from mild effects of vapour leak”.
Independent unionist MLA Claire Sugden said she believed staff had been evacuated, adding: “I commend the creamery on their quick response and the Fire Service for reaching the situation very quickly.
“This only goes to highlight the importance of this service in our community, and the diversity of their role in keeping people safe.”