Over 10,000 vehicles including motorcycle were diverted after PWD ordered closire of the bridge for indefinite period.
The cracks were first seen by rickshaw pullers who carry fishes early in the morning.
PWD Executive Engineer Saugata Sarkar said, "We have found flaws in a bearing on a pillar during preliminary inspection."
Inspection will take place at the joint of pillar and lower part of bridge which is possible only by reaching under the bridge.
Sarkar said bridge maintenance is a continuous process and there was no flaw in it.
The defects were noticed at joint of P2 and P3 on the bridge.