Council's operations engineer Martin Duke said council staff discovered cracks in the bridge on Thursday.

He said a five-tonne gross vehicle mass load limit would apply to the bridge at Wonwondah-Toolondo Road until the diversion was complete.

Mr Duke said council was aiming for a diversion along the side of the bridge to be available from late Friday morning.

He said the diversion would be suitable for all traffic, up to full B-Double sized trucks, provided they were travelling slowly and carefully.

"Traffic will be one way, controlled by traffic signals," he said.

"We are placing signs on the approaches to the bridge."

An expert will inspect the bridge early next week, with load testing to follow.