The short-list was more than doubled on Tuesday, from four parties to 10. Three Chinese contenders have been added to the list, as well as a Japanese consortium and two Australian firms.
One industry source described the expansion of the list as a "mind-boggling" development at this stage of the contracting process, which is aimed at having the 38 three-car trains delivered between mid-2013 and the following year.
The working group of Government, Dunedin City Council and Dunedin business representatives, established to win some of the construction work, said it was also surprised by the move, but it would not change the focus.
"We are still trying to ascertain why the number of tenderers has been expanded, because it doesn't fit with what we expected to happen," group chairman and Otago Chamber of Commerce chief executive John Christie said.
"Having said that, we will work with any company that has the potential to win the contract.
"What we'll be looking to do is identify who those six new companies are and make contact with them in the same way we did to the initial four short-listed."
The four initial companies short-listed are Hitachi Ltd (Japan), Hyundai Rotem Company (Korea), Bombardier Transportation Australia Pty Ltd (Australia) and Construcciones y Auxiliar de Ferrocarriles and Mitsubishi Corporation (Spain and New Zealand).
Representatives from all but Hitachi have expressed interest in visiting Dunedin to see the city's experience and capability in train building.
KiwiRail chief executive Jim Quinn said the company decided to expand the short-list because it wanted to ensure a superior whole-of-life supply and maintenance deal.
