Four people have been injured after lightning struck a rugby goalpost at a Hamilton school and jumped into neighbouring classrooms.

Waikato police Senior Sergeant Tina Shaw said four adults were injured when the lightning bolt struck.

It appeared that the lightning bolt struck a rugby goalpost before travelling along the ground, connecting with the fence of the school's tennis court before hitting the classroom and striking the four teachers.

The incident happened about 1.30pm at Hamilton North School.

Advertisement

The lightning strike left about a dozen burn marks across the school grounds.

The four injured had since been transported to Waikato Hospital, however Shaw confirmed their injuries were not serious.

A hospital spokeswoman said at 5.30pm three of the teachers had been discharged, while one was still under observation.

Lightning bolt fried alarm system and internet

Hamilton North principal Tony Kane said there was a loud crash and bang at 1.30pm just as the children had returned to class after lunch.

Kane said there was a "massive" lightning strike along with a "huge bang at the same time".

Almost simultaneously, the school's smoke detectors have gone off in all of the school's rooms.

"And we thought 'Well gee, there's something that's really struck here'. We went off and checked out to make sure everyone was safe, and everyone kept very calm ... a few staff have complained of having tingling down the sides of their arms and we have called the St John Ambulance and they've sent them very quickly.

"It was louder than anything we've ever heard before so we knew it was really close. But we hadn't realised it was that close.

"It struck the goalpost as you can see and affected the rooms although it's a fair way away. It's shaken the rooms and it's done enough to fry the alarm system and the internet in the school.

"It's hit there (the post) and come back on an angle."

Three staff and eight children were in the classroom at the special needs school at the time.

They were taken to hospital complaining of tingling up their bodies.

A fourth teacher who was in a classroom at the opposite end of the school - about 300m away - was worst affected and was also hospitalised.

The children have been checked by St John and will be monitored by their parents.

Kane said it was lucky the children were inside when the lightning happened and that it hit the rugby post on the field rather than a classroom.

Immediately after the lightning, the children in the classroom that had what Kane described as an "electric shock" were moved into different classrooms and their parents were contacted.

'Shaken and tingly'

A St John Ambulance spokeswoman said staff were called to the Warwick Ave premises after reports of a lightning strike that had injured four people.

The spokeswoman confirmed the four injured were all adults and all in a moderate condition.

The victims were left feeling "shaken and tingly" and were taken to hospital for precautionary checks.

Ambulance staff were checking that the children who were in the classroom at the time were all okay.

Police had since left the scene and the school was now closed for the day.

Hamilton has been lashed by thunder and lightning today.

Neighbours Alan and Anne Pellow heard a loud bang about 1.30pm.

"It shook the house," Anne said. "There was a bit of lightening before that. I just thought it was thunder and it was the loudest thunder I had ever heard."

A few minutes later ambulance and police arrived.

"The kids sounded pretty upset. More upset than usual."

A Warwick Ave resident told Stuff she saw a flash of extremely bright, blue-coloured lightning just before 1.30pm.

"It was a loud cracking sound. It sounded like a gunshot. I have just never experienced anything like it."

Heath St resident Royce Flynn was enjoying a cup of coffee when he felt an "unbelievably very powerful strike and ... vibration" before seeing "a sudden bright flash".

"I was in the lounge with a cup of coffee. It was unbelievable, big flashing, big rumble ... I didn't realise it hit four adults. I hope everyone is okay."

Today's lightning strike follows a period of intense rain yesterday in Hamilton which saw dozens of residents evacuated when 10 homes flooded. Five properties were uninhabitable due to sewage overflows.

'Atmosphere was primed to ping'

MetService meteorologist Georgina Griffiths said followers on social media commonly posted pictures of damage from lightning strikes, often to fences.

There had been 72 lightning strikes recorded over Waikato between midnight and 3pm and, in this instance, the goalposts would have acted as a natural conductor.

A severe weather watch had been in place for the area for several days, with thundery conditions caused by a combination of humidity at the surface and cold temperatures aloft.

"So the atmosphere was primed to ping," she said.

Lightning was the discharge of electricity from thunderstorms and could occur within a cloud, between clouds, or between a cloud and the ground.

But by international standards, lightning did not occur frequently around New Zealand.

However, lightning strikes could injure or kill people and livestock, damage property and infrastructure, and, although rarely in New Zealand, spark forest fires.

According to Statistics New Zealand, between 2001 and 2016, the New Zealand region received about 187,000 ground and sea strikes each year.

Parts of the West Coast in the South Island had the highest annual average density of ground strikes, up to 40 per 25sq km a year.

Parts of the Taranaki, Waikato, and Bay of Plenty regions were prone to lightning, with an annual average of up to 16 ground strikes per 25sq km a year in some areas.

Thunderstorms were expected to increase in frequency and intensity with climate change.