Residents in Tauranga are bracing for another deluge after torrential rain in the early hours of today caused major flooding to homes and businesses.
MetService is forecasting further thunderstorms and possibly small tornadoes.
A storm alert was also in place for Auckland and Hamilton by weather analysts.
About 100 homes were flooded this morning and a further 200 millimetres of rain was forecast for the western Bay of Plenty.
Newstalk ZB reported the city council was handing out sandbags in Mount Maunganui.
Heavy rain and flash flooding caused havoc for homeowners earlier today.
Some drivers were trapped in half submerged cars this morning, with water up to the windows.
Bettie Monroe clothing store owner Helen Fraser said it was not the best start to the school holidays.
"The beautiful art shop next door is flooded, Starbucks across the road is flooded, a number of restaurants and cafes and shops are all flooded.
"So all the shop people are just out mopping. As I open the back door to our shop, I just see our whole shop is under water.
"But not only is it water it's also mud and soot because it's just drained right down to our back entrance and gone straight into our back door, all through out shop."
Emergency services are now over the hump of the flood-related calls, after being swamped with than a hundred incidents this morning.
Northern fire communications shift manager Steve Smith said the rain started about 3am and by 6am nearly 75mm had fallen.
"It came down in one bucket load - it was amazing."
He said by 7.30am the waters were starting to recede and were starting to flow out through the drains "which were obviously blocked and couldn't handle the flow".
It would not be known how much damage was caused until the water was totally drained away.
There had been no reports of injuries, Mr Smith said.
A Mount Maunagnui Fire Station spokesman said this afternoon people were busy mopping up.
He said crews from around the area were called in to cope with the calls that started early today.
"There was all sorts of things like basements flooded and sewage (facilities) flooded, and some trucks went to help people trapped in cars."
He said there were also some minor vehicle crashes because of the flooded roads.
The rain had slowed through the day to drizzle, he said.
Meanwhile, WeatherWatch.co.nz said it was monitoring a storm as it tracked across Auckland this afternoon.
A torrential downpour is currently growing in size and pushing in to Auckland from the north - it is now affecting the North Shore and West Auckland - and is tracking south through the central city towards South Auckland, it said.
"While a few rumbles of thunder have been heard our main concern is with flooding.
"We are now extending our Storm Alert to cover all of Auckland City and Hamilton City."
Motorists and residents should be aware the downpours could produce localised flash and surface flooding.
Conditions were expected to ease later this afternoon and evening, WeatherWatch said.Mount Maunganui Fire senior station officer Lindsay Nicol said flooding was widespread throughout the area.
"There are little pockets throughout the place with problems, it's ongoing. If this rain carries on I can see it happening all day."
Mr Nicol said firefighters from Te Puke, Omokoroa and Katikati had been called in to assist with all the flooding callouts.
"It's a reasonable size event, a lot of it involves flooding in low lying garages and commercial properties. In a lot of cases there's not a lot we can do, most of the water will eventually drain away."
Tauranga police Acting Senior Sergeant Steve Hindmarsh said other flooded areas had included the Mount Maunganui side of the Tauranga Harbour Bridge.
"That was almost entirely closed due to the flooding. We had reports of cars floating in the floods around Ocean Beach Rd and the fire brigade were having to push cars to the main land. A few houses had water go through them.
"There were also many streets in Papamoa that were impassable and localised flooding at the State Highway 2 and Domain Rd roundabout, that was closed early this morning."
Mr Hindmarsh said no injuries had been reported.
"It's the sort of weather where if you don't have to go out, stay at home. A lot of vehicles have been causing trouble driving through the floods, causing a huge wave and letting water go into people's houses."
Tauranga City Council acting communications manager Frank Begley said wastewater overflow had been reported at the Nikau St pump station and as a result, some untreated sewage may have discharged into the harbour around the Pilot Bay area and possibly at the Waikareao Estuary at Third Ave.
He advised people to stay out of the harbour if possible in these areas and apply caution. Tanker trucks were dealing with the issue.
Metservice media meteorologist John Law said 200mm was forecasted to fall along the Western Bay coast until midnight tonight.
He said moderate to heavy rainfall was likely throughout Bay of Plenty, not just in the western part of the region, again on Sunday and Monday.
"People are advised that this amount of rain is likely to cause streams and rivers to rise rapidly, surface flooding and slips. In the Western Bay of Plenty, particularly intense thunderstorms could bring very heavy localised downpours."
