A transformer on fire in Cavendish Drive, Manukau. Photo / Jayson du Toit

In Tokoroa, Kauri St and West Parkdale St in the Waikato town were closed following the lightning strike which felled a large tree and sent flames shooting up from the trunk.

"Actual flash and a bang inside. That was pretty radical. If I hadn't seen and heard it myself I wouldn't have believed it could happen," one person tweeted.

There was also a gas leak in the area.

A police spokesperson said they were assisting Fire and Emergency NZ at the scene and people were asked to avoid the area.

The North Island's west coast was hammered by about 8000 lightning strikes in the early hours this morning.

MetService meteorologist Tui McInnes said since midday yesterday to 8.40am this morning 8643 lightning strikes have been recorded.

"That is across the whole country, so that does include places in the West Coast and down in southern Otago, but the vast majority of the lightning strikes have been in the northern area.

"The majority have been offshore, but as lots of people have noticed this morning as the front spreads over the country, quite a few of those thunderstorms have spread on to the country with that," he said.

"The main areas that are experiencing thunder and lightning are Manawatu, Taranaki, Waikato, Auckland and Northland."

A schoolboy trudges his way to Auckland's Pakuranga College through the downpour on Friday morning. Photo / Jason Oxenham

Earlier this morning MetService meteorologist David Miller said thunderstorms were concentrated on the coast from Kāpiti north to Waikato, with many occurring offshore.

The area was under a severe thunderstorm watch to 9am, with added potential for strong wind gusts over 110km/h, very heavy rain over 20mm per hour, hail and possibly one or two small tornadoes.

Miller said there had been no reports of tornadoes nor hail so far.

The thunderstorm potential would extend to Auckland by midday, and likely clear the country by this afternoon.

Auckland was forecast a high of 16C today with rain from mid-morning, and forecasts of a squally thunderstorm, easing to one or two showers early afternoon as northwesterlies turned southwest.

Behind the severe weather was a series of fronts and troughs moving on to New Zealand from the Tasman Sea.

Mt Taranaki, Tongariro National Park and hill country from Taranaki to Lake Taupō, including Waitomo and the headwaters of the Whanganui River were under a heavy rain watch to 2pm today.

There was also potential for heavy rain in the Tararua Range.

A tree struck by lightning landed on a car in Tokoroa. Photo / Sharyn Newman

Meanwhile in the South Island, snow was forecast on many of the alpine passes.

MetService had issued road snow warnings for Porters Pass (State Highway 73), Lindis Pass (SH8), Crown Range Rd and Milford Rd (SH94).

The snow was coming with a southerly change moving up the South Island, Miller said.

"It will bring showers to areas as it passes through, but it won't be a complete write-off."