Napier Mayor Kirsten Wise has declared a state of emergency in the city due to widespread flooding.
Residents are being told to shelter at home and avoid driving where possible.
"If you feel unsafe at home, self-evacuate to family and friends first. If you have no other options, evacuate to Kennedy Park at 11 Storkey Street, Marewa. If you need urgent help because you are in danger, call 111," a Hawke's Bay Emergency Management statement said.
About 100mm of rain fell between 12pm and 8pm. Photo / Paul Taylor Hawke's Bay Today
A health warning has also been issued in Napier after polluted wastewater burst through manhole covers as the city was hit by flooding.
Monday's deluge also led to a controlled release of polluted wastewater into a stream that flows into the Ahuriri estuary, to take pressure off Napier's bulging stormwater system.
About 100mm of rain fell between 12pm and 8pm on Monday, and more than 126mm was expected to fall before midnight.
Napier CBD flooded, and several slips occurred on Hospital Hill and Bluff Hill.
The rising floodwaters trapped residents in their homes, and vehicles.
A Napier City Council statement said manhole covers were beginning to lift, and the escaping water would have caused a public health risk.
The decision was taken to release pressure from the wastewater network and discharge wastewater, at 5:45 pm this evening, into the Purimu stormwater stream, which flows out to sea through the Ahuriri Estuary.
Medical Officer of Health Nick Jones said floodwaters could carry bugs that cause disease from the ground surface and sewerage systems.
Dr Jones said people should not eat any food that had been in contact with flood waters.
"Children should be kept away from flood waters and from playing in puddles, which may have been contaminated by sewerage."
Hawke's Bay Regional Council, the Hawke's Bay District Health Board and Mana Ahuriri were notified of the discharge.
The council's environmental team will monitor the stormwater network as well as at several other locations to provide baseline data. Testing will be ongoing for a number of days.
Earlier in the day, firefighters rescued a 75-year-old woman trapped in her flooded Lighthouse Rd, Bluff Hill home during pouring rain.
Napier's CBD was flooded by 5pm on Monday. Photo / Warren Buckland
Hawkes Bay firefighters were responding to multiple callouts caused by flooding in the Napier area on Monday night.
Fire and Emergency NZ Area Manager Ken Cooper says 14 urban and rural crews were responding to more than 150 calls for assistance, mostly from people in Napier city.
"We are triaging calls for assistance for homes flooding and roofs leaking , and have removed some elderly from their homes to stay with relatives," Cooper says.
"Hawkes Bay's Urban Search and Rescue team is assessing a number of landslips on Napier hill caused by the heavy rain.
"People should stay home and dry, and travel only if it is essential. If they need assistance please call 111," Cooper says.
"We are working very closely with Napier City Council, Police and Hawkes Bay Civil Defence tonight."
Earlier, firefighters had rescued elderly residents trapped in their homes and taken them to the safer houses of family in the area, a Fenz spokeswoman said.
"We've had reports of flooding and leaking roofs, mostly in the Napier CBD," she said.
A large slip caused by heavy rain on Hospital Hill, in Napier. Photo / Warren Buckland
"There have been a lot of landslips along Napier Hill, and USAR (Urban Search and Rescue) are currently assessing their likely impact to houses in the area."
Cars were stranded in flooded waters and residents were urged to stay inside as roads in the city were no longer driveable.
"At one stage crews were responding to 80 calls for help in the city, mostly flooding and some leaky roofs and there were some gas leaks reported," the Fenz spokeswoman said.
"We're advising people to stay at home and keep dry. Stay inside your house."
A large landslide has also been reported near Havelock Rd, on nearby Hospital Hill.
MetService meteorologist Rob Kerr says the broad low pressure system currently over the North Island was expected to linger until it was pushed eastwards by a ridge of high pressure.
"From now through to later on Wednesday, parts of the North Island will see heavy rain or showers, with thunderstorms and hail possible, while strong or gale south to southeast winds affect the lower North Island," he said.
