The Da Yang 15 was allegedly guilty of other serious violations. It did not declare its shark catch and did not have "bird-scaring devices", which are required to stop seabirds from being caught in long-lines.
It was also not reporting to the Western and Central Pacific Fisheries Commission's (WCPFC) satellite monitoring system.
Records show that both ships were previously flagged to Vanuatu. They changed their flags to China in March.
The Da Yang 15 was previously called Fong Kuo 3. That ship is on a Greenpeace blacklist, which accuses its owners of "fish laundering".
The environmental organisation said the vessel had covered up illegal activity by "fudging their documents" - changing names or the areas in which they were fishing in their log books.
New Zealand authorities have reported the vessels to China to investigate because they were outside New Zealand waters.
The Southern Bluefin Tuna are controlled by the Commission of the Conservation of Southern Bluefin Tuna which China is not a party to and none of its vessels can legally catch the fish.
A spokeswoman for the Ministry of Primary Industries would not say which countries were involved because it could undermine the investigations. In total 37 vessels flagged to six different countries were boarded during the patrol.
"All countries involved have assured the New Zealand authorities that investigations are being carried out and will report back to us and the WCPFC as soon as they are completed."
The countries in question were required by international law to investigate and apply sanctions if required.
New Zealand authorities only have jurisdiction to investigate illegal fishing within New Zealand's waters, but it can take further action if it is unhappy with any sanctions by the country to which a vessel is flagged.
The serious violations were also reported to the Western Central Pacific Fisheries Commission, which has oversight of the area in question. Neither of the vessels had licenses to fish there.
The boats were caught during Operation Zodiac, a joint Royal NZ Navy and Ministry of Primary Industries annual operation on the high seas north of New Zealand.
Labour MP Rino Tirikatene said New Zealand should ensure China took the necessary sanctions.
"We need to apply pressure on China to blacklist their own boats that are fishing on the high seas."
New Zealand and China had cooperated in illegal fishing in other areas, including the Southern Ocean where China recently seized a catch of toothfish from a vessel.
However, it comes at a tense time for Chinese and New Zealand trade relations after reports China had threatened trade reprisals over a complaint about dumping of Chinese steel in New Zealand.
Those reports have been dismissed as "unsubstantiated rumours" by the Government but Zespri has confirmed it was one of the companies approached by Chinese industry figures.
China announced last week it was toughening up checks on kiwifruit exports after detecting a fungus on some New Zealand kiwifruit.
