Two people have been taken to hospital and five more treated after reporting breathing difficulties at a Sainsbury’s.
About 150 people evacuated the store with several other premises within a 50m cordon also cleared.
A cordon had been placed around the store on Longbridge Lane in Longbridge, Birmingham, after emergency services were called shortly before 10: 00 BST.
Sainsbury’s said the store was closed while it assisted the investigation.
The wider cordon was lifted at about 13: 30 BST, with only the Sainsbury’s store remaining behind the barrier.
West Midlands Fire Service described the incident as involving “hazardous substances” and said the supermarket would remain closed for ongoing investigations.
West Midlands Ambulance Service (WMAS) said it was alerted to reports of six people suffering with breathing problems at the shop, with seven treated at the scene.
Two people were taken to hospital as a precaution, it said, while others described as “worried but well” received advice from ambulance staff.
Specialist fire service officers are using air monitoring equipment inside the store to try to establish the cause of the incident.
A nearby college building was not evacuated, the fire service said, but was advised to keep windows closed as a precaution.
People were advised to stay away from the scene.
A spokesperson for Sainsbury’s added that safety was the supermarket chain’s highest priority.
“Anyone who has been in the area and is feeling unwell should seek medical advice as a precaution,” WMAS added.
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