New Zealand will have to forge a new trade agreement with the UK while making sure free-trade negotiations with Europe remain on track, Labour's Foreign Affairs spokesman David Shearer says.
The UK has voted to leave the European Union, causing turmoil in world financial markets and triggering the exit of UK Prime Minister David Cameron by October.
"While we respect the decision to leave the EU, it goes without saying the move will usher in a massive period of uncertainty in Europe, in the financial markets and in the United Kingdom itself," Mr Shearer said.
He said it would create real uncertainty for Kiwis in the UK and EU.
"As the second largest economy in the EU, a member of the Security Council, and as a close ally of the US, Britain's loss will also be keenly felt across the EU," he said.
The process of exiting is likely to take at least two years.
Prime Minister John Key said New Zealand respected the UK's decision and would continue to have a strong relationship with the EU and the UK.
New Zealand remained committed to the launch of formal negotiations on a free-trade agreement with the EU.
"In terms of our existing trade arrangements, the immediate effects of the leave vote on New Zealand are likely to be limited and we expect that trade and other business activities will continue smoothly in the interim," Mr Key said via a spokesperson.
Federated Farmers is urging New Zealand to be first in seeking a new trade relationship with the UK, and sees opportunities.
New Zealand First leader Winston Peters said the situation of New Zealanders living in the UK may improve.
"I think the British will reach towards New Zealand, Australia and Canada. And the second thing is our young people will get a fair go in the UK in the future," he said.
Young New Zealanders in the UK were in demand but were being treated like second class citizens, he said.