An Auckland ferry company is blaming a rogue wave for injuring two of its passengers on a ferry headed for Waiheke.
The incident happened on Explore Ferry's 9.30am service, while Auckland was in the midst of an hour-long downpour in which 20mm of rain fell.
Explore Ferry operations manager Megan Watson said two women were among a group of 20 midwives and went out for air because they were feeling sick.
However, a rogue wave hit while they were outside, knocking them off their feet.
"One woman has a suspected broken leg. Paramedics were called from the boat. It took about 35 minutes for the paramedic on Waiheke to reach the boat and during that time our staff administered first aid to the woman," she said.
Ms Watson said winds were blustery but were up to only 25 knots at the time.
An internal investigation was under way and the incident would be filed with Maritime New Zealand.
The rain was part of the wild weather which hit the upper North Island today, hammering it with heavy rain and gale-force winds.
It closed roads and schools on the Coromandel Peninsula, and flooding in Auckland disrupted travel this morning, closing Tamaki Drive.
A MetService spokesperson said Auckland city got 20mm of rain in one hour this morning, and in Coromandel, 107mm was recorded in a 12-hour period.
Skies clearing for Auckland behind a cold front, but watch for a few convective showers. IR image from the JMA ^TA pic.twitter.com/A8ipYAa10m— MetService (@MetService) August 31, 2015
New Zealand Transport Agency (NZTA) has reported serious flooding on SH1 between Brynderwyn and Otaika and urged drivers to take extra care, although the road remains open at this stage.
The Fire Service said a man had to be rescued from his vehicle after heavy rain caused flash flooding in parts of Auckland.
It said the man was freed after about 20 minutes trapped in his car in Onehunga.
A Fire Service spokesperson said it had had had about 20 weather-related call-outs this morning, mostly in central Auckland.
Auckland's Tamaki Drive has reopened after being completely flooded from Judges Bay through to Ngapipi Road. Motorists passing through are being urged to take extreme care.
Tamaki Dr is down to one lane in each direction due to the flooding. Please expect delays and take extra care. http://t.co/MwnFx38x6h— Auckland Transport (@AklTransport) August 31, 2015
The Gulf Harbour ferry did not sailing this morning, and the service was replaced by buses.
Heavy rainfalls overnight also caused surface flooding and minor slips across the Coromandel, according to the Thames Coromandel District Council.
State Highway 25, from Tairua to Whangamata, is closed due to flooding, as is State Highway 23, from Hamilton to Raglan and at Cogswell Road near Thames.
Heavy rain has also flooded up to nine other roads near Thames, with State Highway 39, from Ngaruawahia To Pirongia, reduced to one lane.
Senior Sergeant Andrew Townsend said there were reports of minor slips on the Thames Coast and Kopu-Hikuai Roads but they remained open at the moment.
He said Hikauai School was closed for the day, and several school bus services were not running.
Motorists were urged to avoid any unnecessary travel in the area.
On the South Island's West Coast, civil defence in Buller is advising people to stay indoors as the south easterly winds threaten trees and power lines.
Whitebaiters on the West Coast were also being warned to take extreme care and avoid riverbanks where possible, as king tides could lead to dangerous conditions.
In the longer term, farmers are being warned to brace for major El Nino weather that could significantly increase rainfall in some regions, and cause drought-like conditions in others.
MetService meteorologist Georgina Griffiths told Morning Report it was a "rough and tumble" start to September and New Zealanders could expect cool temperatures for the rest of the month.
She said the El Nino weather effect would not kick in until the end of spring, and there was plenty of stormy weather to get through yet.
But she said the westerly winds would then pick up and dry out the eastern areas.
"The Tasman Sea has started to help us now, with some solid rain, and if they get a drink now it will help, but it will be a slow drying out as we head towards Christmas."