The Automobile Association (AA) has revealed the peak days for people travelling.
It said people traditionally return from their holidays on 2 and 3 January - the peak days for travelling.
AA chief policy officer Simon Douglas said the biggest traffic hotspots were expected to be north and south of Auckland, as that was where there were "the biggest population centres".
Douglas said there could also be some congestion around Wellington, although the opening of Transmission Gully had seen traffic flow improve "considerably" in recent years.
"If you can leave before 10am in the morning or after 4pm in the afternoon, you'll avoid the worst of those peaks," Douglas advised.
Douglas said a huge maintenance programme had also been rolled out by the government this summer, further affecting traffic.
He said there had also been "quite a bit of variation" in the weather conditions over the Christmas period and there were heavy rain warnings ahead.
"If you're planning to drive through those events, please if you can avoid being on the road at the worst of times."
If people did have to drive in adverse conditions, he advised that they allowed extra journey time and keep an adequate distance from the car in front of them.
MetService said rain would be approaching the western part of the country from the later part of Thursday and into Friday.
Heavy rain watches were already in place for several parts of the South Island and Mount Taranaki in the North.
MetService said more wind and rain watches could be added.
Holiday road toll
The Christmas holiday road toll has risen to seven following the death of a woman in a quad bike crash in Waikato.
Emergency services were called to Rauparaha Street in Marokopa late yesterday afternoon, after witnesses reported seeing her come off the bike.
Last year, 21 people died on the roads over the Christmas-New Year holiday period.