Sixty-four homes in the Mangahauini River catchment and Tokomaru Bay township have been evacuated out of precaution.
Tairāwhiti Civil Defence controller Ben Green said with the rain forecast for Thursday night, there is an immediate risk of the failure of the debris dam upstream of the township.
"The incoming rain amplifies the risk given the ground is very unstable and saturated following the damage done by Cyclone Gabrielle," Green said.
Green said the community is being evacuated to local marae or to whānau in areas outside of the affected area.
"Our Civil Defence team on the ground in Tokomaru Bay went door to door this afternoon. The safety of our people is paramount."
Green said experts are being brought in to assess the dam site and provide options that could alleviate the risk.
"The evacuation is supported by Tairāwhiti CDEM and the police."
Green said a community hui will be held at the Tokomaru Bay club rooms at 6pm on Thursday.
"We want to make sure everyone stays well-informed and that this evacuation is well-managed."
Roadblocks have also been set up to stop access to areas of concern around Mangahauini River catchment and Tokomaru Bay.
Gisborne's yellow heavy rain watch has since been upgraded to an orange heavy rain warning from 9pm Thursday to 2am Saturday.
"Expect 80 to 130mm of rain. Peak rates of 10 to 25mm/h, especially in thunderstorms," MetService's website said.
Coromandel Peninsula is also under an orange heavy rain warning from 4am Friday to 4am Saturday.
"Expect 100 to 140 mm of rain. Peak rates of 20 to 40mm/h in thunderstorms with possible downpours."
Meanwhile, Hawke's Bay authorities are preparing "for all eventualities", including evacuations, following MetService's orange heavy rain warning.
In a Facebook post, Hawke's Bay Civil Defence said it is working with the regional council and emergency services to plan and prepare for further heavy rain just days after Cyclone Gabrielle.
MetService's orange heavy rain warning came into effect at 10am on Thursday and will end at 10am on Saturday.
MetService expects 150 to 200mm of rain about the ranges and away from the range north of Hastings, with 75 to 100mm elsewhere.
"The heaviest falls are likely from 3pm Friday, with peak rates of 20 to 30mm/h."
The Civil Defence said hydrologists are comfortable the major rivers in the region will remain within their existing channels, "but we are not taking any chances".
"Emergency repairs to the stopbanks damaged last week are underway or are complete. We are augmenting the river monitoring network with people on the ground who will be monitoring critical areas in person from tomorrow, including overnight."
The Civil Defence said the triggers of an evacuation are still being discussed, but if evacuations are needed a mobile alert to affected areas will be issued.
"We will also publicise any evacuation orders over radio and all broadcast and online media."
It acknowledged the anxiety among the Hawke's Bay community with impending further rain following Cyclone Gabrielle.
Hawke's Bay Civil Defence's advice:
- Keep up with the weather forecasts from MetService
- Listen to advice from the Regional Council about river levels, particularly if you live in a floodplain
- Talk to the others in your household and make a plan for what you will do if the rain causes flooding.
- Pack a grab bag with clothes, medical supplies and things that are special for you
- Make a plan for your pets too
- If you feel unsafe at home, you don't need to wait for an official warning to evacuate
- It's best to go to whanau or friends, but our Civil Defence centres are open for those who need them.
