Emergency services have responded to a "chemical incident" on the Wrexham Industrial Estate.
North Wales Fire and Rescue said the incident occurred following a "reaction in an industrial process".
Multiple fire crews were called to the scene in the early hours of Friday morning.
Witnesses described a strong smell in the air around the industrial estate which lies east of Wrexham.
North Wales Fire and Rescue said the site had to be fully evacuated as crews dealt with the incident.
The products involved have now been contained and the incident is in its closing stages.