A spout of flames and a bang marked a significant post-earthquake milestone as the railway between Christchurch and Picton was rejoined.
The chemical weld was just like the hundreds of others needed to get the track up and running, but the pressure was on for the crew as 160 KiwiRail workers, appearing as a sea of orange hi-vis, watched from the coastline on Tuesday.
For Paul "Jonesy" Jones, it was an emotional moment seeing the badly-damaged line rejoined.
We've just been working about eight months solid, so it was a big milestone really." The scale of the devastation had been "a big eye opener", he said.
By the end of the month, freight trains will be able to run on the partially repaired line. It will take some pressure off the alternative State Highway 1, which has been overrun by a volume of trucks it was never built for while the coastal highway remained closed.
KiwiRail chief executive Peter Reidy said two freight trains would run each night initially, which was about 60 per cent capacity compared to pre-quake volumes.
It would take about 2000 trucks a month off the alternative highway, he said.
"When you think about the [alternative route], you think about the safety issues on the road, there was a fatality unfortunately just last weekend, so 2000 trucks off the road is significant for New Zealand, and I'm sure the local communities will be happy too."
The initial opening would be restricted to low-speed, low-frequency services.
About 150 kilometres of line has been made ready for trains, including 5000 new concrete sleepers being laid, 12km of track being rebuilt and 5km of track realigned, Reidy said.
He said the work was "at least three months ahead of schedule".
KiwiRail rail protection manager Paul Andrews said the track had been rejoined using a chemical weld called a "one shot thermic weld". The process got to about 3500 degrees Celsius.
Sparks flew for about 15 minutes as the molten metal joined the lines, but the entire process took about 90 minutes.
Andrews said it was one of hundreds of welds required to repair the track. When it was completed "you would never know the weld was there".
Last November's earthquake caused major damage to about 60 sites along the rail line, including tunnels, bridges and embankments.
The Main North Line carried about 1 million tonnes of freight annually before the earthquake. The link will not be fully operational until mid-2018.
Meanwhile, work continues on repairing the adjacent State Highway 1, with efforts moving from earthmoving to roading construction.
The vital highway is expected to be open to traffic before Christmas, though repair work will continue after it opens. A significant upgrade including a cycleway was announced in July.