A spokesman for the Community Safety Bureau at Steelhouse Lane police said: “The Bullring remained closed in order that the fire service could fumigate the operations centre.

“The incident is not being treated as suspicious and appears to be due to fumes from a cleaning product.”

The Bullring remained closed today, and bosses said its closure would have cost businesses tens of thousands of pounds.

John Lamb, spokesman for Birmingham Chamber of Commerce, said: “This is devastating for the city centre, we have fantastic retail sector here.

“This is a very serious thing to happen whatever the cause. It is really disappointing especially at this time.

“I know the Bullring footfall has been holding despite the economic problems and I really hope this does not have a knock-on effect on that.”