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
Overnight it will be cooler and fresher but most places will stay dry with a nippy start to Sunday.
X Factor contestant Raign seems to impress the Wembley audience with her own song even though Cheryl finds her "really annoying".
YouTube superstar Alfie Deyes got a sense of how far he has come when thousands of fans descended on his latest book signing in London.