Emergency services have been monitoring the centre's air systems
Birmingham's Bullring shopping centre remains shut to bank holiday weekend shoppers after a chemical incident affected more than 30 people.
The centre has been shut for two days, but managers say they are working to try to reopen later on Saturday.
It was evacuated on Thursday after shoppers and staff reported symptoms including minor respiratory problems.
Bullring managers said they were "continuing to work with the police to investigate the incident".
Tim Walley, Bullring general manager, said: "The investigation has been ongoing throughout the night and we hope to have the issue resolved soon.
"We are working towards Bullring reopening today, but our priority continues to be staff and visitors to Bullring.
"The centre will open when all internal checks have been completed and we are assured the centre is in a position to welcome back staff and visitors. "
Staff at the centre who turned up for work on Saturday were reportedly sitting outside in the sunshine waiting to be told what was happening.
The Bullring provides over 110,000 sq m (1.2m sq ft) of retail space with more than 160 shops and kiosks inside.
When it opened in 2003, 8,000 jobs were created.
Professor Isabelle Szmigin of Birmingham University, said the uncertainty was damaging the centre.
"It is this feeling of uncertainty and not knowing that is damaging them," she said.
"It would be much better to give regular updates even if the updates were saying sorry, we do not know what is happening."
She added the smaller businesses, such as the kiosks and independent traders, could be badly hit.
John Lamb from Birmingham's Chamber of Commerce, said the closure could lead to large financial losses for the shopping centre.
"Clearly, it will cost tens of thousands of pounds in lost trade if it remains closed," he said.
West Midlands Police said the cause was a suspected petro-chemical-based contamination, possibly in the centre's ventilation or air conditioning systems.
They also said they did not know if it was the result of an accident or malicious act.
The centre closed on Thursday, reopened briefly on Friday, but was evacuated again after some members of staff staff reported shortness of breath and nausea.