However, despite the challenging conditions they found themselves in, the engineers managed to pull the man up a steep riverbank before emergency services arrived on the scene.
The incident unfolded at a bridge over Saltwater Creek, near Redruth St, Timaru, South Canterbury, around 3.30pm on Monday.
Quested said the pair had been walking a dog on the beach at the end of Saltwater Creek when they decided to take a shortcut and walk across the railway bridge.
As they were making the crossing, a train came around the bend towards them.
One man managed to get off the bridge with the dog, but the other was not so lucky.
He was hit by the train and knocked into the creek.
Hato Hone St John said it sent an ambulance, a helicopter, an operations manager and a rapid response unit to the incident.
The man was airlifted to Christchurch Hospital in a critical condition.