Air New Zealand says flights operating to some airports east of Mt Tongariro may be delayed because of the eruption.
And Airways, the company which operates air traffic control, said a no-fly zone of eight miles around the ash cloud is in place.
It said the cloud appears to be moving quite quickly.
Tongariro police have urged motorists to take extra care if they travelled to the area today to view the volcanic activity.
There were some road closures after the eruption but these were lifted fairly quickly and police were pleased the road network remained congestion-free for the rest of the afternoon and evening.