Civil Defence director Sarah Stuart-Black said while the worst of the weather had passed for most regions, there was still a danger from rivers in places such as Edgecumbe as the water made its way through catchments.
"It is possible that delayed flooding will occur as higher-than-usual water volumes flow
through the catchments and through the river systems. Caution around waterways through the next few days is recommended," Stuart-Black said.
Aerial assessments were under way this morning to check the extent of damage across the Bay of Plenty.
Stuart-Black urged people to try to delay any non-essential travel for today because of the need to do repairs on roads and to be careful of flooding and slips over Easter.
Bay of Plenty recorded 12.5 metre wave height at 6pm. #CycloneCook pic.twitter.com/oO9OXJUFAp
— MetService (@MetService) April 13, 2017
Fire and police were dealing with calls to flooding, downed trees and power lines and several local roads were closed as was State Highway 1 in Seddon.
There were also widespread power outages in Whakatane, Edgecumbe and Ohope, as well as rural Gisborne and Hawkes Bay. Water and wastewater systems were also damaged in some areas.
• Those travelling should allow extra time, keep up to date with road and weather information and be prepared for "challenging" driving conditions such as debris and possible detours. "Please, don't take any chances."
• People evacuated should not return to their homes until cleared by local officials.
• Those going into damaged buildings should be careful and check for structural damage such as to staircases, walls and windows.
• Look for and report any broken gas or power lines.
• Further flooding was possible and people should not walk or drive through flood waters
• Take care around waterways and be ready to act, if water is rising, don't wait for an official warning to move.
• The Defence Force would help where required, but extra personnel and aircraft on standby were likely to be stood down later today if not needed.
She said it would take "weeks and months" for the areas most badly affected by Cyclone Debbie and now Cyclone Cook, such as Edgecumbe and parts of Whakatane, to recover and "our support will continue."
Although Cyclone Cook had not had the impact feared on areas such as Auckland and Bay of Plenty, she said it was still a dangerous event and important to take precautions.
"Because people took from those precautionary messages, the impact from the storm is less likely to have been what it could have been. So we are really pleased. We should never under-estimate the potential severity of events like this."
MetService's Chris Noble said Cyclone Cook tracked slightly further east than earlier expected, which meant eastern Bay of Plenty, Gisborne and Hawke's Bay were worst affected.
Auckland and Wellington escaped the worst of it.
"Had the system tracked a little bit further west I think it would have been a very different story for the likes of central and western parts of the North Island, including Auckland and Wellington."
This morning it was off the Canterbury coast and heading toward Otago before it moved to the south. All severe weather warnings had been lifted but a number of severe weather watches were in place and there were strong winds off the Banks Peninsula and heading to eastern Otago.
Watches were in place for heavy rain in eastern Otago, Buller and Westland through to tomorrow.
Metservice was keeping a close eye on East Otago.