"In short, we're ready to welcome the world back."
Ardern said the border was already open to New Zealanders - and on Monday eligible critical workers were allowed in without isolating.
People already with visas, but outside the visa waiver list, would become eligible to enter New Zealand on May 1.
For people from outside visa waiver countries, the major issue was how to process new visas in a timely way, Ardern said.
The PM said the Government wanted to clearly signal New Zealand was keen to supercharge its economic recovery.
Ardern said New Zealand was a safe place to visit, adding transtasman travellers were crucial to the domestic tourism sector.
"They will be able to arrive in time for the Australian school holidays."
Those travellers will also help boost the ski season, Ardern said.
Visitor numbers would be lower than in 2019 and travellers would need to return negative rapid antigen test results.
Ardern said she knew from speaking to tourism operators how tough the past two years had been.
"Thank you for the hard yards you did for all of us."
The National Party said moving forward the reopening date for international tourists was overdue but welcome news.
But the party said visa processing delays were absurd.
National's Covid-19 Response spokesman Chris Bishop said allowing fully vaccinated travellers to visit would help New Zealand properly reconnect with the world.
"Airports, airlines and the tourism sector have been crying out for a reopening date for weeks now," Bishop added.
National's tourism spokesman Todd McClay said tourism could thrive again.
"However, today's border announcement was silent on tourists from countries who require a visa to travel to New Zealand," he said.
McClay said not allowing these tourists to visit because Immigration New Zealand could not process visitor visas was "a new level of government incompetence".
He said the Government had had two years to prepare.
"Yet again [Immigration Minister] Kris Faafoi has dropped the ball," McClay said.
Act Party leader David Seymour said the remaining rules would be impossible to enforce with tourists.
"Vaccine passes, isolation, importing rapid antigen tests and QR codes will look quaint to people from countries that have already moved on, and trying to enforce them will only show how nonsensical our own rules are," he said.
"We will now have a situation where a tourist with a negative test is free to get the first taxi out of Auckland Airport, but a household contact has to isolate for seven days.
"Opening the border makes our isolation rules look stupid because they are."
Tourism operators are hoping tourists will flock back for the winter holidays.
Tourism Industry Aotearoa communications manager Ann-Marie Johnson said the best hope would be to welcome Australians back for the April school holidays, incorporating Easter and the upcoming ski season.
She told The AM Show she didn't expect to see significant visitors from the rest of the world until next summer, but the announcement would allow people to be able to start making plans now.
Johnson said some operators may not reopen, or may have lost some employees to other industries, but she hoped they'd also see the new opportunities awaiting.
Cruising in
Ardern said the Government was working on how to ensure new rules would be consistent with maritime borders, and she expected cruise ship visitors to return at some point.
Ardern said the system was likely to evolve in time, for example, to consider how unvaccinated people overseas could visit New Zealand.
If visiting Australians visiting fell ill with Covid-19, they would be as well cared for as possible.
Ardern added: "They would want to be prepared...if you need to stay in one place because you're sick."
She said visitors would receive a welcome pack and rapid antigen tests.
A critical element of the plan was reuniting visitors with regional economies, the PM said.
Ardern said she would focus, during her international engagements, on promoting New Zealand's major exporters.
"We know Covid is still with us and will be with us for some time," Ardern added.
But she said New Zealand could now start a new chapter.
"We will be a sought-after market."
Ardern said announcements about vaccine mandates and passes will be made next week.
She indicated vaccine passes would be less justified after the Omicron peak.
Ardern said the Government already indicated rules around vaccine passes and the traffic light system would be reviewed.
Ardern made the announcement with Tourism Minister Stuart Nash, who is appearing by Zoom - Nash is isolating because some household members have Covid-19.
"This is the most exciting moment [in the] tourism sector for the past two years," Nash said.
Nash said the ski season would commence in June, and traditionally, about 70 per cent of foreign ski tourists were Australians.
"Australians are going to be well looked after and we're going to love seeing you."
Nash said global experience showed tourism had been slow to bounce back in foreign markets.
"We're not expecting pre-Covid numbers in a great hurry."
Nash said the head of Heathrow Airport had said it might take five years for a return to pre-Covid travel numbers.
Today's announcement modified the plan set out this year.
That plan was for vaccinated travellers from Australia and visa-waiver countries to come in by July, and those from the rest of the world from October.
New Zealanders returning from overseas are already able to return without isolating, provided they test negative.
Ardern had said last month that reopening dates would be brought forward if viable – and that would depend on when the Omicron outbreak peaked.
Rapid tests
Covid-19 Minister Chris Hipkins has also announced nearly a million more rapid antigen tests will be available for schools and early learning centres.
He did not hold a press conference because he tested positive this morning on his seventh day of isolating as a household contact.
Hipkins must now isolate for a further seven days.
