The foreign fishermen who've tested positive for Covid-19 in Christchurch were given a recognised test before boarding the plane.
Eleven have returned positive results at the Sudima Hotel and 14 other cases are under investigation.
They're among 440 fishers from Russia and the Ukraine, 270 of whom are due to go out on three Independent Fisheries boats next month.
Air Commodore Darryn Webb told Chris Lynch on Newstalk ZB's Canterbury Mornings that numbers of infected people were expected to increase.
"I think it's logical to expect that. We knew in the planning that places like Russia are high risk."
Director general of health Ashley Bloomfield would update at 1pm, he said.
He 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.