Health officials are still examining CCTV footage as to how the community case could have been transmitted through managed isolation.
Speaking in a press conference on Tuesday, COVID-19 Response Minister Chris Hipkins explains why the Government hasn't been able to stop returnees from mingling.
"Getting to New Zealand from anywhere in the world at the moment is a complex web of travel," he says.
"It's a bit of a melting pot out there in terms of COVID-19 because any plane landing in New Zealand is likely to have passengers in it from a variety of different locations."
Hipkins says health authorities are already trying to keep people from the same plane in the same facilities.
"We're always looking at how we can refine that better, how we understand the risks of different flights coming in more so that we can respond to that but it's not cut and dry - there's no very simple answers here," he says.
"The investigation into the source is still continuing and that includes the review of CCTV footage and so on to try and identify how the transmission between the two people may have occurred."
An epidemiologist and infectious disease expert says the Government should look into building specialised MIQ facilities.
Dr Michael Baker said the hotels we're using at the moment are functioning "reasonably", but they're not designed specifically for quarantine.
"They are functioning reasonably but we may see problems with ventilation and people mixing," he told The Project on Monday.
Dr Baker said an alternative could be to build specialised quarantine facilities near military airports.
"It might be quite a good investment for the future, given we're going to get other pandemic diseases on the horizon."