New Zealand Prime Minister Bill English has criticised the Turnbull government's newly unveiled citizenship changes, expressing concern that tens of thousands of New Zealanders would now have to wait years longer to become Australian citizens.

The "special relationship" between the two countries needed to be maintained, Mr English said, adding that government officials were seeking to understand the impact of the changes on a streamlined pathway to citizenship unveiled last year for New Zealanders living in Australia.

There is concern among Kiwis that the changed citizenship conditions – specifically the longer, four-year waiting period before being eligible – undermine the pathway finalised last year by Prime Minister Malcolm Turnbull and former prime minister John Key.

"I wouldn't agree it completely undermines it just because the deal was put in place and there is a path to citizenship and that wasn't there before Prime Minister Turnbull agreed to put it in place, but it is disappointing for them – for the Kiwis [in Australia] and for ourselves – that it looks like it will take longer," Mr English said in a press conference on Monday.