A gas-like smell around ANZ's South Dunedin branch caused emergency services to descend on King Edward St about 2pm as people began feeling nauseous from the fumes.
A St John spokeswoman said two people suffering from nausea were taken to Dunedin Hospital.
Dunedin City fire station Senior Station Officer Jason Hill said the street was blocked for about an hour as firefighters used gas-detecting equipment to find the source.
There were initially fears flammable gas had leaked, but these eased when none was detected.
''What we found was no lpg leaking, but what they call an odorant which they put in lpg to make it smell,'' Mr Hill said.
The odorant came from an old unused gas line which ran under the street.
It leaked out because of the rain and lack of wind.
''If there was a slight wind no-one would ever know it. It would just blow away.''
Odorants, typically ethyl mercaptan, could cause headaches and nausea, but were not a serious danger.
Contractors who were called in used an odorant-neutralising product to counteract the odour and the street was reopened about 3pm.
Ann Sell, who works next door to ANZ at DTR, said her colleague was treated by ambulance staff after feeling the effects of the fumes.
''She went pale and her eyes went glassy ... and she kind of started slurring [her speech],'' Ms Sell said.
Ms Sell said she, too, was affected by the fumes and was suffering from a headache and ''a bit of a queasy stomach''.
