Webb said it was not an "uncontained outbreak" and something that happens in our facilities.
The processes were robust and fit for purpose.
"We have an exclusive use facility for these fishermen. Part of the process early on is that we do know they are coming from a high risk area so let's provide them a single location."
He said there was a 24-hour delay as the aircraft worked through its process in Moscow and the fishermen were assembled there for 48 hours and then en route for 18 hours.
That period of time provided an opportunity for the virus to spread.
"That could well be an exposure risk factor."
Webb said the quarantine procedures are "absolutely" working.
The Ministry of Health said it was investigating after the cases were detected during routine day three testing.
None involved cases in the community, it said.
The ministry said the positive cases were part of a group who were the only people staying at the facility.
The crew were mostly Russians with others coming from Ukraine. Russia has recorded more than 1.3 million cases of Covid-19 - the fourth highest number of any country.
Webb said we need to expect that anyone who comes across the border may present a risk.
"The infection prevention and control measures are consistent across the board.
"What we've seen in this case is just a number of covid cases, the same system is in place, it is just at a bigger number."
No changes to border exemptions being considered at this point
"The situation with fishing crew shows NZ's border management systems are working as they should and demonstrates why strict border management, testing and isolation procedures are critical to our Covid response."
"We put them in an exclusive facility, we translated the welcome packs into Russian, we have brought in translation services on site and we operate at level 4 to keep everyone safe," Immigration Minister Kris Faafoi said
One hundred fishing crew have arrived on commercial flights since September, he said.
"We will just continue to work with the fishing companies. At this stage the next and the final chartered flight is due to land on November 2nd. Based on what we've seen in this instance, we might make some changes but it's to early to make those calls now."
Authorities were going through medical details of the crew and will likely find out today if the crew were in fact tested before they left Russia.
Seafood New Zealand CEO Jeremy Helson said the incoming fishermen were all Covid tested before boarding the charter flight into New Zealand.
"All crewmen tested negative. This pre-flight test was beyond what the Government required. While we await to see how many cases there are, the fact that they were all detected in quarantine shows the system is working well."
Helson earlier said shore-bound vessels would be costing Sealord, Independent Fisheries and Maruha Nichiro tens of millions of dollars.
A New Zealand fishing executive has praised the government's quarantine system.
Yesterday eleven international fisherman tested positive for Covid-19 at the Sudima Christchurch Airport hotel MIQ, while 14 cases are under investigation.
Sealord chief executive Doug Paulin says the news demonstrates the effectiveness of the government's Covid-19 prevention systems.
He said the outbreak is not disappointing and that his company is happy the government has strict protocols in place.
Of the 440 foreign fishermen in isolation, 110 are due to work on Sealord boats.
The first port of call for his company is to follow up on the health of the individuals involved.
He said Sealord is making sure the individuals involved are healthy and that the economic position of his company is not a priority at this time.
Long-term risk needs to be addressed - epidemiologist
Epidemiologist Professor Michael Baker says it's unusual so many people in a managed isolation facility tested positive for Covid-19 if they isolated and were tested before arriving into New Zealand.
However he says we shouldn't be concerned.
"We're seeing imported cases pretty much every day in New Zealand and just looking at the last few weeks for example, we're seeing an average of about two imported cases a day going into managed isolation/quarantine facilities.
"Obviously what we're seeing here is a lot more cases in one day than usual."
It's part of an ongoing pattern where people who are testing positive have come from overseas - reflecting the fact that the pandemic has intensified in many parts of the world, Baker said.
This number of people testing positive at once is manageable but could become a problem if high numbers become very ill, he said.
"I think the wider issue is the long-term pattern and that is that every time we import a person who is positive to this virus, that is an added risk to our system."
Over time the risk adds up, he said.
"Travellers from countries which have a very intense pandemic with a lot of transmission present, we need to look at steps before they travel to New Zealand to reduce that risk."
-additional reporting, RNZ
