Residents of a small seaside village near Hastings have been cut off as heavy rain swamps Hawke's Bay.

The road from Hastings to the nearby community of Ocean Beach was closed due to flooding about 7pm on Wednesday .

Hastings District Council said it was likely to remain closed overnight. Residents who were unable to get home and could not make stay with family or friends should call the council or 111 if they were stranded in an emergency.

Meanwhile, Napier residents have been told to avoid baths and to think twice before flushing toilets as the city's wastewater system struggles to cope.

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Napier City Council told residents the wastewater system had been "overloaded" by 24 hours of torrential rain.

ROSS GIBLIN/STUFF Many Hawke's Bay roads have been affected by surface flooding.

"We're asking Napier to please keep their household wastewater to a minimum for the next 36 hours," the council posted on Facebook.

"Do not take baths or flush toilets unless absolutely necessary, keep showers short and leave the washing and dishes for another day. This will help us get back on track."

The council's aging wastewater system was overloaded during the heavy rainfall of ex-Cyclone Debbie in April 2017.

That led the council to discharge about 2,500,000 litres of stormwater and wastewater into the Ahuriri estuary, in a "controlled" release to avoid an uncontrolled release with a higher impact to the community.

Earlier on Wednesday, heavy rain forced the closure of a Hawke's Bay school as a slow moving storm continued to hammer the region with rain.

Staff at Pukehou School, beside State Highway 2 30km south of Hastings, informed parents just after midday that they held concerns about heavy flooding in the area. They asked that all children be collected "as soon as possible so we can ensure that everyone arrives home safely".

The New Zealand Transport Agency advised the Napier-Taupo Rd (SH5) was down to one lane due to a slip near Pohokura Rd.

There was surface water on most state highways, including Tutira to Wairoa, Pakipaki to Waipukurau, and Fernhill to Tikokino.

Slips and swollen rivers caused numerous road closures in Hastings, including Makahu Rd at the Ford, Aropaoanui Rd, Ellis Wallace Rd, Kereru Rd, Mackenzie Rd and Salisbury Rd.

WARWICK SMITH/STUFF Napier residents have been told to think twice before flushing their toilets.

The Hawke's Bay Civil Defence Emergency Management Group said more than 100mm of rain fell in some areas over Tuesday night and a further 100mm was forecast to fall before 2am on Thursday.

"Most of this in the hill country or coastal hills. HB Regional Council are not overly concerned at these predicted levels," group manager Ian Macdonald said.

"However, there will be localised surface flooding, slips and small streams may overtop their banks. Driving conditions may be hazardous."

Heavy swells were expected ast the system moved on "so be careful at the beach over the next few days," he said.