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.
More top news
Instagram is celebrating its fifth birthday just weeks after smashing the 400-million-user mark.
European judges have found French restrictions on prisoners' voting rights are legal, a decision likely to be welcomed in Britain.
Princes William and Harry found themselves being called something they perhaps hadn't before when they appeared on DIY SOS.