Constable Jay Morriss, of Oamaru, said the Conroy Removals truck became stuck about 10.15am, when the driver misjudged the 3.5m clearance height of the rail bridge while travelling south towards the intersection with Itchen St.
Contractors working just metres from the bridge helped free the truck, which was empty at the time, by partly deflating its tyres.
The driver was able to reverse the vehicle out of the predicament, albeit not smoothly.
A witness, who did not want to be named, said he had a feeling the truck might come to grief when he saw it approach the rail bridge.
"I thought this one would be close and then it stopped and made a bang. It was a bit of excitement for the day."
The driver, who was not injured, declined to comment.
The southbound lane was closed for about 30 minutes.
Kiwirail staff inspected the bridge and found no issues.
In July 2018, a southbound H&J Bruce Transport Ltd truck struck the bridge, stopped and toppled on to its side, blocking the northbound lane.
In 2014, a northbound New Zealand Vehicle Deliveries Transport Ltd transporter truck carrying several cars also came to grief.
Two cars, including a black Audi, were shunted off the truck and badly damaged.