Health Minister Tony Ryall says it will be a challenge for district health boards to meet a new, tighter timeframe for treating cancer patients.
Only two years ago patients routinely waited 12 to 13 weeks to begin treatment or were sent to Australia.
However, he says the boards are determined to meet the targets.
Mr Ryall was speaking at the opening of a linear accelerator in Auckland on Monday.
He said that from January the target for patients who needed radiation treatment would drop from within six to within four weeks.
He said four weeks was the international standard.
He also said that since March, the Northern Regional Cancer Centre had treated between 80% and 90% of patients within four weeks. Hard work, careful planning and use of the private sector had turned waiting times around.
He said four weeks covered variations between different types of cancers, ensuring all people got treatment within a clinically acceptable and safe timeframe.