Heavy rain warnings for Bay of Plenty and Coromandel will remain in place overnight - but the risk of flooding has fallen.
Campers at several spots were earlier moved to high ground as a precaution after overnight flooding.
Civil Defence said it did not expect to see any road closures overnight, but says there is still a risk of surface flooding.
It said motorists in the affected areas should drive to the conditions, and if possible, avoid getting behind the wheel until tomorrow morning.
More than 100mm was recorded in less than 24 hours in parts, leading to the evacuation of flooded campsites on the Coromandel Peninsula.
Civil Defence has moved campers to higher ground in Coromandel and closed a freedom camping carpark - the Rhodes reserve in Thames - with fears of flooding as more heavy rain is forecast.
MetService has issued a heavy rain warning for Northland, Coromandel Peninsula, Bay of Plenty and Gisborne from Tolaga Bay northwards, while a heavy rain watch is in place for Auckland and Waikato. Heavy rain warnings are in place for the Coromandel Peninsula until 8am tomorrow.
Campers at Opoutere Beach Coastal Camping on Coromandel peninsula's east coast and Kuaotunu Campground have been moved.
Jacob Spence, who runs Opoutere Coastal Camping, said campers who had not headed home had been moved to higher ground.
"Quite a few have left, one of our areas which is prone to flooding, I've already moved everyone yesterday, so everyone's organised, got all their water, their battery lights are all ready."
About 150 Bay of Plenty campers from the Waihi Beach and Beach Haven Top 10 holiday parks were evacuated because of flooding early this morning.
Ian Smith, who runs both campsites, said they are fully booked from Boxing Day so hopes the weather gods are compliant.
"The phone's ringing off the hook with everyone predicting we're going to be very wet and muddy and they don't want to come.
"We can't predict what the weather's going to do over the next 24 hours, we hope and trust that it will clear away, we'll get a little bit of breeze and it will dry out the sites fairly quickly, most of the sites aren't too bad at this stage."
The area's Civil Defence controller, Garry Towler, earlier said they were trying to get campers to move on, or move to higher ground.
"For residents of the Coromandel it's just business as usual, but we have thousands and thousands of people who have come on to the peninsula.
"We just have to get an advisory to them, the quickest way we can, to just say be aware of what's going on."
Mr Towler said it was the perfect storm as 100mm of heavy rain meets high tides and limited drainage options.
"We're just advising people to keep right up to date with the weather and to make alternative plans. It's just a short, risky period of time that we face.
"Don't try to force your way through and take unnecessary risks, it's just not worth it because this will be clearing by later tomorrow."
"If you're driving around please take care, there's potential with some of the intense rainfall to cause some surface flooding maybe even flash flooding" - Meteorologist Andy Downs
Meteorologist Andy Downs told Summer Report the forecast was far from the festive weather people would be hoping for.
"People in all those regions, which also of course quite popular tourist spots at this time of the year, people need to be prepared for some fairly intense rain."
He said motorists should also take caution as the intense rain created potential for surface flooding and flash flooding.
"The areas of concern are eastern parts of Northland, northern parts of Auckland but particularly Coromandel, Bay of Plenty and maybe even those northern parts of Gisborne, where we could see a further substantial amount of rain over the next 24 to 36 hours."
Meanwhile, a section of State Highway 1 near Kaikōura is down to one lane due to a slip.
The Transport Agency says road users between Kaikōura and Cheviot can expect minor delays as traffic management is in place.
The slip is blocking one lane about 5km northeast of Goose Bay.
Mount Maunganui's base track has also been shut until further notice due to slips and debris.
Tauranga City Council said at this stage all other tracks on the mountain were open.
Early this morning, about 150 campers at two Bay of Plenty holiday parks were evacuated because of flooding.
Emergency services were called to the Waihi Beach and Beach Haven Top 10 holiday parks just before 3am.
Police said campers were evacuated and taken to the Waihi RSA.
There were no reports of injuries.
MetService expected the severe weather to spread south across the North Island between tonight and tomorrow, bringing periods of heavy rain and possible thunderstorms to the northern districts.
However, Mr Downs said there was possibly some relief for those at the top of the North Island tomorrow.
"This main rain band we're talking about is going through today - Christmas Eve - particularly overnight and early Christmas morning but later through [tomorrow] morning the main rain band will clear and the top of the North Island might actually start to see some sunshine but it will be mixed with showers and possibly even some thunderstorms."
Lower South Island place to be on Christmas day
On the other hand, the lower part of the South Island looked like the best place to be for Christmas with Central Otago enjoying some sunny skies today.
The good weather is predicted to continue tomorrow for the lower South Island with temperatures of 30 degrees expected in some areas.
Meteorologist James Millward said it was looking like Wanaka would be the hottest spot in the country with 31 degrees predicted.
"Christmas Day itself is looking really nice and fine if you're down through Southland, Otago, Dunedin, Westland - you're going to have a really nice day and temperatures kind of approaching 30 degrees through there."
As for the top of the South Island and the lower North Island, it looked like it would be a gloomy day tomorrow with on-and-off rain, Mr Millward said.
The outlook for New Year's Eve at the moment predicted some strong westerly flows and possibly showers in the west but the eastern areas looked good, Mr Downs said.