A large slip which has created a lake between Wairoa and Gisborne is being monitored.
Hawke's Bay Civil Defence Emergency Management Group is working with local authorities to monitor the growing dam of water and sediment sited on the regional boundary between Wairoa and Gisborne.
The landslide, likely triggered by a small localised earthquake earlier this month, has resulted in approximately 80 million tonnes of material forming a large dam on Mangapoike River (a small tributary to the Wairoa River).
The new lake is about 50 metres deep and rising.
The area affected by the landslide is 25.8 hectares and the landslide is still moving.
No water is currently leaking from the dam, but it is rising by about 60cm each day.
Hawke's Bay Civil Defence Group Manager Ian Macdonald said the slip has become a significant hazard and people are warned to stay away from it.
"Downstream landowners and river users are strongly advised to keep out of the riverbed."
The landslide and dam are located on private property and in a remote area, but authorities want local people and downstream communities to be aware of the hazard risk.
Wairoa District Council and Civil Defence staff have been talking directly with potentially affected residents.
The dam might fail at any time and there is a significant amount of water behind the landslide, he said.
"We're working closely with Gisborne and Wairoa district councils, with support from Hawke's Bay Regional Council to assess the risk of dam failure and develop an ongoing management plan.
Specialised engineers engaged by the Hawke's Bay Regional Council were due on site on Thursday.
Paparatu Rd is closed to the public because of this and appropriate signage has been installed.
There is no date for when the road will reopen at this stage.