The newest stretch of line in the country's railway network has been officially opened.
The 700 metre line, with a further 600 metres of siding, links Fonterra dairy co-operative's new Darfield processing site in Canterbury to the main trunk line.
It will allow Fonterra to transport hundreds of thousands of tonnes of milk powder a year to the Port of Lyttelton by rail instead of road.
Since the Darfield plant started operating last year, about 20 trucks of milk powder a day have travelled the road to Lyttelton.
A second second drier is under construction and production is due to triple from August.
Fonterra's South Island operations general manager Robert Spurway says the rail line will allow it to take 90 trucks a day off the road.