Heavy rainfall overnight has caused further damage to main routes closed because of Cyclone Gabrielle, including the Napier-Taupō Rd, State Highway 5, where a 30-metre section of road has dropped away.

Hawke's Bay Civil Defence Emergency Management Group says a slip has moved further, taking out both lanes near Te Pohue and Glengarry and making the route impassible.

Waka Kotahi Hawke's Bay/Gisborne system manager Martin Colditz confirms part of the route has suffered 'extensive damage” following more heavy rainfall in the area overnight.

Roading contractors are onsite.

”The slip caused by Cyclone Gabrielle has moved further overnight, making that drop out larger,” he says.

Waka Kotahi emergency response spokesperson Mark Owen​ says slips and trees could continue to come down even in dry conditions, because of the saturated ground.

'A lot of the roads are in fairly tenuous states. There will be one lane sections and speed restrictions. A lot of work is required to get them back to normal.”

All of the state highways are 'lifelines” for their communities, but reopening the Napier-Taupō Rd is a priority.

'We're really focused on reopening that sooner rather than later,” says Owen.

Without the road, there's a lot of pressure on State Highway 2 and SH50 as the only freight routes into Hawke's Bay.

It's hoped an update on the Napier-Taupō Rd, indicating when it might reopen, will be provided later this week.

Further north SH35 and the Napier-Wairoa route, will be two of the 'most challenging” to reopen, says Owen.

Access to the community of Clydebank, near Wairoa, remains cut-off along Mangapoike Rd and SH38 after a big slip fell across the road.

The section of the highway through the Mangahauini Gorge, just north of Tokomaru Bay, has turned into a river.

The cyclone debris formed a dam containing around 400,000 cubic metres of silt, trees, and water. The Mangahauini River diverted around the dam and onto the state highway.

A video from Tairāwhiti Civil Defence shows the river flowing over what remains of the washed-out highway.

Waka Kotahi crews are in Hawke's Bay and Gisborne, assessing the damage and repairing where possible, but the double-whammy of Cyclone Hale followed by Cyclone Gabrielle is making the clean-up 'pretty challenging”.

They are dealing with working in 'already soggy ground” and knowing that more rain could change everything.

Temporary Bailey bridges will be brought in where they are needed, but places where bridges are washed away, the challenges are often bigger than simply replacing a bridge.

No precise timelines are available on state highways reopening, but Waka Kotahi is planning to give 'early indications” once assessments are complete.

Owen asks anyone driving in affected areas to be careful, especially if rain is forecast.

'There will be delays. Be patient. Make a contingency plan for if your route is blocked.”

He also asks people to listen to the advice of road workers – Waka Kotahi is 'disappointed” to hear of incidents where workers were abused.

'If a road's closed, it's closed for a reason. That's usually because it's too dangerous for the public to use.”

State highway closures in Hawke's Bay and Gisborne

SH2: Ōpōtiki to Gisborne is closed due to slips and flooding.

SH35: Ruatorea and Tikitiki is closed due to an overnight slip.

SH35: Te Puia Springs to Tolaga Bay is closed. At the north end is the dam causing the Mangahauini River to flow over the road. At the south end of the closure, the Hikuwai Bridge is washed away.

SH35: Gisborne to Tolaga Bay is open. Drivers should take extra care as slips, trees, and debris remain.

SH38: Lake Waikaremoana to Wairoa is closed.

SH2: Wairoa to Gisborne is open with speed restrictions and traffic management.

SH5: Napier to Taupō is closed.

SH2: Napier to Wairoa is closed.

SH51: Napier to Hastings has one lane open at the Clive Bridge. There are significant delays at peak times.

SH50: Hastings to Takapau is now open with speed restrictions. Take care.

- Erin Gourley and Gianina Schwanecke/Stuff.