Photo: 123RF
The country's cyber watchdog is warning about a mass hacking operation called Salt Typhoon.
Blamed on China, it has sparked briefings in the US of the president and senators.
Hackers were able to listen to telephone conversations and read text messages, and had swept up masses of metadata from Americans' online activity - and had not been expelled - US authorities have warned.
In New Zealand, the National Cyber Security Centre put out an advisory on Wednesday alongside US authorities.
This came several weeks after the FBI warned that Salt Typhoon has been embedded in major telcos for more than a year.
"This advisory details the best protection against a People's Republic of China (PRC)-affiliated threat actor that has compromised networks of major global telecommunications providers," the NCSC said.
"New Zealand organisations operate similar networks to our international partners so we encourage New Zealand telecommunications and other organisations with on-premises enterprise equipment to apply the best practices outlined in this guide."
The alarm went up about the cyber espionage in America several months ago.
However, it has now sparked classified briefings of the US President Joe Biden and senators.
A senior but unnamed US official was quoted by Reuters on Thursday saying: "We do not believe it's every cell phone in the country, but we believe it's potentially a large number of individuals that the Chinese government was focused on."
"They have not told us why they didn't catch it; what they could have done to prevent it," Republican Senator Rick Scott expressed frustration with the briefing.
Giant telco Verizon said it became aware several weeks ago that a "highly sophisticated" attack had got into its networks.
The advisory on Wednesday is the latest of several such warnings in the last couple of years about cyber attacks the New Zealand government has, in an increasingly forthright way, blamed on the Chinese state.
RNZ has asked the Chinese embassy for comment.
Chinese officials have previously described the allegations as disinformation, Reuters reported.
Headlines like that in the Washington Post a year ago, 'China's cyber army is invading critical US services', are becoming more common.
Sign up for Ngā Pitopito Kōrero, a daily newsletter curated by our editors and delivered straight to your inbox every weekday.