It's likely another government tried to attack the Reserve Bank, a cyber security expert says.
The Reserve Bank of New Zealand - Te Pūtea Matua said this afternoon it was responding "with urgency" to a breach of one of its data systems.
In a statement, the bank said a third party file sharing service it used to share and store some sensitive information had been hacked.
Professor of Computer Science at Auckland University, Dave Parry, said the attack was significant.
It was likely to be another government trying to attack the Reserve Bank, he said.
"Because ultimately if you were coming from a sort of like criminal perspective, the government agencies aren't going to pay your ransom or whatever, so you'd be more interested probably coming in from a government to government level."
Parry said cyber attacks were very common now and it was likely there will be more like this.
Data system taken offline
Governor Adrian Orr said the breach had been contained, the bank was acting with urgency and treating the matter with the highest priority.
"We are working closely with domestic and international cyber security experts and other relevant authorities as part of our investigation and response to this malicious attack," he said.
"The nature and extent of information that has been potentially accessed is still being determined, but it may include some commercially and personally sensitive information."
Orr said the system had been secured and taken offline until the bank had completed initial investigations.
"It will take time to understand the full implications of this breach, and we are working with system users whose information may have been accessed. Our core functions remain sound and operational."
Several major organisations in New Zealand have been the target of cyber attacks in the past year, including the New Zealand Stock Exchange which had its servers knocked out of public view for nearly a week in August.