More than 300 emergency calls as torrential rain and thunderstorms batter North Island

Heavy rain and thunderstorms have battered parts of the North Island on Tuesday.

Fire and Emergency received more than 300 weather-related calls for help between 8am and 6pm on Tuesday - with the vast majority in Auckland.

Police reported more than 250 weather-related jobs between midday and 4.30pm.

A local state of emergency was declared in the country's largest city as flooding quickly occurred once again after heavy storms in January and Cyclone Gabrielle in February.

The weather caused gridlock across the city as commuters tried to get home early.

Mayor Wayne Brown made the declaration from Sydney, Australia where he was on council business when the flooding began.

Brown passed on his responsibilities to deputy mayor Desley Simpson - and was expected back in Auckland around midnight, cutting his trip short.

The torrential rain has since moved away from Tāmaki Makaurau but residents were being urged to remain vigilant as it could come back.

Auckland Minister Michael Wood said people should keep a close eye on updates from Auckland Emergency Management (AEM) overnight.

He said the key advice was to stay home if possible, take extreme care if out on the roads, and check in on those who may need help.

Wood said there was a taskforce currently looking at the ways the city should grow, and where houses should and should not be.

AEM said periods of heavy rain and thunderstorms remained possible but thunderstorm warnings across the region had been lifted except for Aotea / Great Barrier Island.

AEM duty controller Parul Sood said it was important to remember that even as the weather improved, not all streams and rivers had reached their peak.

"It can take time for the rain that has fallen in the hills to make its way down stream. Therefore, some waterways may still be rising even though the rain has eased.

"Any more heavy rain could cause surface and/or flash flooding around streams, gullies, and urban areas."

She asked people to stay away from waterways and floodwaters.

Thirty Rapid Building Assessment teams were expected to start carrying out rapid building assessments throughout the Auckland region from tomorrow morning, Sood said.

Although Civil Defence Centres and Community Shelters were opened, few people needed to use them, she said.

MetService said an orange heavy rain warning was in place for Bay of Plenty and Rotorua until 3am.

Meteorologist Georgina Griffiths earlier said the back edge of the rainfall was now through Auckland and the risk of the high intensity downpours had reduced.

Everywhere in Auckland had experienced between 30 and 35 millimetres of rain in an hour or less on Tuesday.

Bay of Plenty

Torrential rain hit the Bay of Plenty later in the day, with Rotorua recording over 65mm between 3pm and 5pm.

There were reports of flooding in Rotorua and the council said it had been getting numerous calls for help.

MetService said up to 100mm of rain was possible for the Bay of Plenty region.

"Rainfall rates of 10 to 15 mm per hour likely, but possibly 15 to 25 mm per hour in thunderstorms."

On Tuesday evening, Bay of Plenty Civil Defence said in a post online "The good news is, there are no reports of anyone hurt. The bad news is, there is more rain to come later this evening."

What happened overnight will depend on the amount of rain. Roading contractors, utilities teams and emergency services were "flat out".

Tauranga City Council said downed trees and surface flooding were causing traffic delays and unsafe conditions and it was monitoring the situation.

While a thunderstorm warning had been lifted, people were asked to avoid any unnecessary travel.

In the Bay of Plenty, State Highway 36 had been closed, as had Cambridge Road due to a slip, which was being monitored by Fire and Emergency.

A tree blocked State Highway 2 before Youngson Road and State Highway 29 was closed but they had reopened by 9pm.

Inland, Rotorua Lakes Council said there was a lot of surface flooding across the district.

Heavy rain was hitting the region as it made its way across the country. A spokesperson for the council said it had crews responding to 24 incidents caused by flooding or trees falling.

The city was hit with 44mm of rain between 5pm and 6pm.

Student missing in Northland

A Year 11 Whangārei Boys' High School student remains missing after being washed away in floodwaters during a school trip to the Abbey Caves.

The other 14 students and two adults who were on the trip were all accounted for.

Police said the search for the student would resume at first light on Wednesday morning.

In a statement, school principal Karen Gilbert-Smith called the event "hugely upsetting for all concerned".

"As a school we are focusing on supporting all whānau, staff and students concerned with this event, and the wider school community, with assistance from iwi and agencies.

"In time we will seek to understand how this situation occurred, but for now I ask that we stay united as a WBHS community and provide support where required."

Road closures

A number of roads have been closed as a result of flooding or slips.

In Auckland, they include Forge Road in Mount Wellington, Ihumatao Road in Māngere and Hendry Avenue in Hillsborough.

Waka Kotahi said State Highway 1 at the Brynderwyns would remain closed overnight following flooding and slips. The closure would be reassessed in the morning.

Click here for a more extensive list of closures in Auckland.

Auckland Transport Group Manager Metro Services Darek Koper advised caution when travelling in the city overnight.

"Train services have now resumed on the Southern and Western Lines, with services running at lower speeds until further clearance is received from KiwiRail. Services on the Onehunga Line remain suspended and alternative transport options are in place between Penrose and Onehunga."

There were still disruptions to buses and ferry services were still affected as well, Koper said.

Travel should begin returning to normal on Wednesday, he added.

Flight disruptions

Several domestic flights were cancelled out of Auckland but disruption was not at the same level the city faced during Auckland anniversary weekend.

At least 10 Air New Zealand flights in and out of the airport were axed and passengers faced some delays.

Auckland Airport was advising passengers to check with their airline app or its website for updated information about travel.