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Heavy rain watches are in place for parts of the North Island - and Marlborough in the south.
MetService said heavy rain and thunderstorms were possible for Bay of Plenty, from Edgecumbe westwards, Gisborne/ Tai Rāwhiti and Hawke's Bay, south of Te Pohue.
It comes as Tai Rāwhiti and Hawke's Bay are still recovering from the devastation of Cyclone Gabrielle.
Tairāwhiti Civil Defence said heavy rain could cause flooding and damage to roads that were already fragile after Cyclone Gabrielle.
The local council issued a flood warning for the Hikuwai River earlier this morning, but said it appeared to have peaked just below nine metres at 7am on Sunday.
Civil Defence manager Ben Green said while there was a lot of water in the river, it was not hugely concerning.
But he said people should still take care on the roads, especially in Uawa/Tolaga Bay.
"It's just wet out there and that's what we are finding, talking to the area coordinator.
"There was power outages and surface flooding on the main road. At this time of the year, it is winter but of course, things are a bit fragile."
Green said more rain was forecast, but they were likely to be intense downpours with breaks which would help ease flooding.
Uawa/Tolaga Bay Civil Defence is urging people to stay off the roads.
Civil Defence manager Greg Shelton said there had been thunderstorms and heavy rain since about midnight.
There were power outages throughout the town overnight but power had now been restored, he said.
"If you don't have to go out, don't go out. If you do have to go out, in a bigger vehicle if you have to, and although at the moment all roads are open, just treat everything with caution and keep your speed down but ideally, just stay home by the fire."
While evacuations were not on the cards yet, Shelton said Civil Defence will be on standby with another day and a half of rain forecast.
Gisborne District Council has opened an emergency sewer valve to stop wastewater overflowing into homes and roads amidst the heavy rain.
The council said the wastewater system has been flooded and pump stations were under pressure with nearly 100 millimetres of rain falling in some parts of the city in the past 24 hours.
It opened the valve at the Gladstone Road Bridge, discharging wastewater into the Turanganui River.
The discharge was highly diluted with rainwater, but there was still a risk to health, so people should avoid fishing, gathering shellfish and water activities.
In Marlborough, heavy rainfall was possible south of Ward.
On Saturday, MetService said: "A low pressure system continues to lie slow moving near the upper North Island tomorrow, directing further periods of rain into eastern parts of both islands."
All rain watches were in place for more than 24 hours.
MetService said the rainfall may reach warning criteria in all areas under watches.