The enormous pressure on contact tracers is expected to ease over the next few days - but only if case numbers drop as hoped.
More staff are urgently being recruited because the system has exceeded its surge capacity with a huge number of contacts to trace.
There were now about 14,000 people considered close contacts - the system was already struggling when it was 9000.
Tracers had contacted only about half of them.
Health authorities said they were being triaged so those most at risk were reached first.
Contact tracing expert and public health professor Philip Hill said the system was likely at its busiest point.
"That requirement for the capacity will probably decrease because the number of contacts per case in lockdown is so much less," he said.
People had to play their part by staying home under alert level 4, he said.
Previously Covid-19 had been easier to trace than some other viruses, like the flu, because it tended to have a longer incubation period, he said.
But the more infectious Delta strain had changed that, meaning some form of lockdown was needed to help contain it, he said.
Auckland's health authorities were continuing to recruit tracers as they received support from regional and national public health units.
Staff across Southland and Otago were helping, with the Southern DHB recruiting more as well.
The DHB said it already had about 60 tracers working, many of them from home across the district.
There were at least 50 contacts in the region, and most of the workers were supporting the effort in Auckland, a spokeswoman said.