A witness believed the air conditioning had exploded, releasing “poisonous gas” inside the store.
The buyers were evacuated shortly before 11 a.m.
It is believed that no one was under the alley where it exploded.
The affected branch is the Newmarket Road hypermarket in Cambridge.
Tesco staff have cordoned off the parking lot and are not letting people in.
Staff gathered in front of the parking lot.
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