Police said the leaked chemical is believed to be hydrochloric acid and that the building, on the site of Chemtura Manufacturing, had been evacuated.
The cause of the leak was not yet known.
Superintendent Chris Ullah from Greater Manchester Police said:
Emergency services are working at the scene to control the leak and motorists are being asked to avoid the area. We will keep the public updated but would ask people around the Trafford Park area to stay indoors for the time being as a precautionary measure.