New Zealand appears to have been settled by diverse sets of Fifields. An early settler on the North Island was Jesse, who came from Haresfield, Gloucestershire. He first landed in Australia where the birth of son John was recorded in 1887, but promptly moved to New Zealand where the birth of Herbert Jesse was recorded in 1888. Early descendants appear especially in Helensville. Being from the Gloucester area, he was most likely related to the Australian and Canadian Maritime Fifields.
The family of early immigrant William Fifield settled in the vicinity of Whangarei, north of Aukland. William appears in the England section of this website, #12829, and is likely related to the U. S. Fifields. Since both Gloucester and Hampshire have hamlets with the Fifield name, it seems likely that Fifields from these two areas are not related through the Fifield surname.
On the South Island, most Fifields appear to be descendants of two brothers, John and Jonas, who came from Oxfordshire in 1875 with their families. Oxford also has a small town named Fifield, so this may well be yet a third unrelated group.
While I have some data on all the New Zealand Fifields obtained from vital records indexes plus a few electoral rolls, it is not sufficient to tie branches together. Assistance from New Zealand researchers would be appreciated.