Prime Minister Jacinda Ardern speaks to striking teachers at Parliament's grounds. - Photo: RNZ / Rebekah Parsons-King
Striking teachers held rallies throughout the country and showed support for a two-day strike if they don't get an improved offer from the Ministry of Education.
The strike closed hundreds of schools, affecting 400,000 pupils.
In the capital, the NZEI representatives warned at a rally at Westpac Stadium that more strikes might be needed. The audience of thousands of teachers showed overwhelming support for a two-day strike if another was held, he said.
After the rally a crowd of about 4000 marched to Parliament grounds, where they were met by Prime Minister Jacinda Ardern, Education Minister Chris Hipkins and other ministers.
Ms Ardern told the crowd she wasn't scheduled to speak but couldn't stay away when she saw protesters streaming onto Parliament grounds.
She said radical change took time and asked teachers to work with the government.
Teacher Matt Boucher told the rally pay rises had barely kept up with cost of living increases, and teachers were more than disappointed, they were outraged.
The NZEI members cheered Mr Hipkins when he said the government had heard teachers' concerns.
Education Minister Chris Hipkins told RNZ the offer to teachers is roughly double what they were getting under the previous government.
"We do absolutely acknowledge that their pay and conditions have not kept up with the demands that they are facing and we will address that."
He challenged the government to make teachers a priority.
In Auckland, thousands of teachers marched up Queen Street to Aotea Square holding placards and chanting, along with their families and supporters.
Many onlookers have been clapping as the march passed.
One of the teachers on Queen Street, Vanessa Short, said she would leave the job if staff get anything less than what the union was demanding.
"Sixteen percent is not unrealistic, if I left and went to Australia I'd get 30 percent more wage. Sixteen percent is nothing. We have had no money and input into our profession for the last 10, 12, 13 years. We've had pathetic, like, one percent rise."
Teachers in Christchurch gathered in Cathedral Square before some set off to march to the Education Ministry offices.
The strike is happening because the negotiation of the collective agreements for primary and intermediate teachers and principals has stalled.
The Education Ministry and NZEI have tried mediation to break the deadlock, but without success.
The union entered negotiations with a claim that included a 16 percent pay rise over two years for primary school teachers, special education coordinators in every school, and smaller class sizes.
But the ministry offered increases ranging from 14 percent over three years for new teachers through to six percent for experienced teachers.
The ministry's offer would raise beginning teachers' pay from $47,980 to $55,030 over three years, while the salaries of the most experienced teachers would increase from $75,949 to $80,599.
The union, the NZEI, said today the offer wasn't enough and that in a straw poll of the protesting teachers, they backed striking for two days.
'Teachers have gone backwards in terms of pay'
Earlier in the day, as the strike started, teachers and supporters went out on the streets in many centres around the country.
Pat Swanson was with a group holding placards and banners at an intersection in central New Plymouth this morning and said teachers felt they'd fallen behind in conditions of work and pay.
"Colleagues are saying enough is enough," he told Morning Report.
"I've been ... teaching full-time for the last 14 years, I've certainly noticed the pressure on teachers with workload.
"At the same time teachers have gone backwards in terms of pay. We're struggling to recruit and retain teachers and as a result of that class sizes are going up too."
He said he earned in the low $70,000s and if he was teaching in Australia he'd be getting 20 percent more.
Read more: Teachers strike: What you need to know.
West End school principal Gary Punler in Palmerston North said he had been teaching for 39 years and the schooling system was the worst he'd seen it, in particular because of the past 10 years of under-investment.
"We don't want to repeat this exercise again, the government needs to listen."
He said principals would earn between $95,000 and $130,000 a year, and in his school class sizes ranged from 28 to 34 pupils.
NZEI lead negotiator Louise Green said the education system was at "a crisis point" and the union hoped to send a very strong message to government that it was time to put money into solving the problem.
The union wants a 16 percent pay rise over two years, special education co-ordinators in every school, and smaller class sizes.