China is New Zealand's biggest seafood export market.
In February last year the Herald revealed China had suspended exports from a Sanford site in Havelock that processes mussels and a Sealord facility in Nelson that processes fin fish and fishmeal for animal feeds.
MPI said at the time the suspensions were due to issues around the interpretation of the World Health Organisation's Covid guidance and food safety management.
Both sites had been subject to live video audits by Chinese Customs.
MPI said the sites had been complying with New Zealand's alert level 1 protocols at the time.
Sealord chief executive Doug Paulin said the financial impact of the continuing suspension was "significant".
"Last year it impacted our net profit before tax by more than 10 per cent."
Paulin said it was unfortunate there had been no resolution, "largely due to complications caused by Covid-19 globally and complicated bureaucratic processes"
"We are continuing to work with MPI and remain hopeful of a resolution in the not too distant future."
NZX-listed Sanford said it was disappointing the company had yet to regain its export certification for China for its Havelock plant.
Chief customer office Andre Gargiulo said the overall impact was not material.
"Sanford has a well-established strategy of diversification of our markets and we supply Greenshell mussels to a number of countries from our plant in Havelock. China was a portion of our exports from there.
"We continue to work closely with MPI on finding a resolution."
Before the pandemic seafood exports returned $713m in 2019, according to industry organisation Seafood NZ. Government figures show returns fell to $400m in the year to October 2020 after the impact of Covid on China's hospitality and retail sector. Greenshell mussel exports to China earned $337m in 2019.
MPI's Ainsworth said the ongoing engagement with China on the seafood suspensions had been constructive.
"... Like any trade matter, we place significant priority and importance on this. We'd like to acknowledge both Sealord and Sanford in working constructively through this matter with us."
On the additional suspension in the unknown primary sector, he said MPI was working with the exporter and China Customs to resolve the matter.
"We cannot provide further information for commercial reasons."