A holiday park in Waihi Beach was evacuated because of rising river levels on Saturday night.
Dozens of homes are flooded along Waihi Beach and in parts of Tauranga, where some residents have already evacuated their homes.
The Western Bay of Plenty was hit by a deluge of rain over 24 hours with firefighters saying some properties were swamped by at least half a metre of water.
The Fire Service said on Saturday night it was concerned about rising river levels at the Waihi Stream bridge next to the Waihi Beach Top 10 Holiday park and was evacuating residents.
It says firefighters were pumping water from houses along Waihi Beach where sections were completely flooded.
Meanwhile contractors are trying to fix a transformer which has been damaged by a large wall that fell onto it because of continued rain.
Elsewhere in the country there has been flooding on Waiheke Island, where water was leaking through the roof of the library.
Tauranga City Council said there were several slips, with the most serious along Princess Street in Otumoetai where contractors were working on the damaged transformer that's been crushed.
The Fire Service and police are door-knocking along a street in Matua to ensure people are safe.
Firefighters are asking residents who are worried about their homes to evacuate, and say some have already left.
Fire Service Northern Communications shift manager Jarron Phillips says there had been at least 50 homes flooded, mostly in Otumoetai and Matua.
A number of roads were closed in the Western Bay of Plenty because of flooding.
State Highway 36, from the roundabout near the crematorium on Pyes Pa Road, to the lakes subdivision was shut off to motorists.
State Highway 2, from Barkes Corner, Pyes Pa Road, to the Oropi Road roundabout, was also closed .
Police say driving conditions are extremely hazardous in Mount Maunganui and Papamoa Beach where there is considerable flooding.
Homes and business were flooded and motorists trapped in cars during torrential rain and thunderstorms during the day.
The Fire Service had to deal with more than 100 callouts from early Saturday morning, with Mount Maunganui the worst affected area.
Extra fire crews were called in from neighbouring areas to help.
One family had to be evacuated from their home down a ladder at 5am after the bottom storey of their home was flooded, the Fire Service said.
Firefighters had to free motorists trapped by floodwater up to car windows.
Helen Fraser from clothing store Bettie Munroe on Maunganui Road said mud and silt went through the back of the shop when a stormwater grate could not cope with the deluge.
Mount Maunganui resident Annie Moon said her lounge floor turned into a pond and she and her partner would have to move out until all the damage is repaired.
Heavy rain is also expected to hit parts of the Taranaki, Tasman and Marlborough regions and to last until Monday. In the South Island, moderate to heavy rain is expected in the Canterbury high country and eastern Otago.