Photo: Supplied by Ministry for Primary Industries
Biosecurity New Zealand says likening an invasive non-native seaweed called caulerpa to a marine version of foot and mouth is perhaps alarmist.
The smothering seaweed is currently found near Aotea Great Barrier Island and Ahuahu Great Mercury Island.
The Northland Regional Council feels not enough is being done to contain its spread, and fears it will destroy recreational and commercial fishing along the east coast.
Readiness and response lead John Walsh agreed caulerpa was invasive, but said Biosecurity New Zealand still did not know how significant a risk it posed.
He said they were working hard to contain or slow its spread, such as banning boats and fishing in infected areas.
''I think we should just pause a little bit before being too alarmist, but at the same time we need to get on with the job that we have been doing for the last two years - which is to prevent the spread of caulerpa from those places in which we know it is currently and to better understand the impacts of caulerpa in New Zealand.
''Our intention is that we continue with those efforts for the foreseeable future and that we look to evolve the programme as well, and it is really timely that Northland has identified Caulerpa as a threat to their region and we will work with Northland Regional Council to do what we can to manage that threat.''
Walsh said Biosecurity NZ had done a lot of work to understand control methods, but prevention tools were limited.
However, in isolated outbreaks local elimination was possible, he said.
''We know that if we find a patch early enough, it's not too big, there's nothing else in the area, there are tools we can apply to get rid of it. So we would certainly be keen to do that, and are keen to talk to the Northland Regional Council about how we do that with them.''
The Northland Regional Council has asked the government for $500,000 annually to do its own surveillance.
Walsh said the four relevant regional councils - Auckland, Waikato, Bay of Plenty and Northland - were meeting soon and funding would be discussed.