New Zealand has marked its darkest day of the pandemic with a record 34 deaths, taking the country's Covid-19 mortality rate past that of the United States for the first time. 

Experts say despite daily case numbers starting to plateau, given the lag in hospitalisations and deaths, that rate could climb even higher over the next few weeks. 

And with case numbers in our biggest city also dropping, a top health official has warned of a "Mexican wave" of infections and regional spikes - with Canterbury and South Canterbury now experiencing a peak. 

University of Otago epidemiologist professor Michael Baker said New Zealand's daily Covid-related deaths per million over a seven-day rolling average were now higher than in the US. 

"At the moment, New Zealand's mortality is moving into the middle or upper range for a high-income country with the exception of Hong Kong, which is extremely high. 

"For the first time now, our daily mortality rate has passed the United States. We won't be in that range for very long, maybe a week or two. It's still a shock for us." 

On March 27, the US' daily mortality rate was 2.3 and New Zealand's was 1.9. Taking into account Tuesday's moving average of 15 deaths, Baker said New Zealand's rate had passed that of the US and now sat at 2.9. 

The US mortality rate peaked around the first week of February at close to 8 deaths per million. 

Most OECD countries were ahead of New Zealand in terms of their Omicron outbreaks and their death rates were dropping as New Zealand's peaked. 

Baker said Taranaki, Whanganui and the West Coast had their highest Covid-19 case numbers yesterday. The numbers in those DHBs were jumping around a lot, he said, reflecting the virus arriving in different populations at different times. 

"The whole country is heading down past its peak, but you are seeing a slightly bumpier ride in Taranaki, Whanganui and West Coast. 

"Smaller, more rural DHBs do seem to be having these slightly bumpier declines, which partly reflects the smaller populations and probably people dispersed over a number of population centres." 

Director of public health Dr Caroline McElnay said the spike in deaths was not unexpected given the wide spread of the outbreak, and some of the 34 people had died over the past 10 days. 

Some included cases where Covid was discovered after the death. 

Some deaths would not be caused by Covid-19, and many people with other conditions were dying from Covid, she said. 

In terms of age, 27 of the 34 people who had died were over 70. 

The previous highest daily death count was 24 on March 16. 

Overall there have been 303 publicly reported deaths with Covid-19. 

The latest information available from the Ministry of Health shows 43 of 266 people have died from Covid-19, while 221 are yet to be classified. 

McElnay said there had been a sustained drop in case numbers. 

Despite yesterday's increase to 17,148 Covid community cases, the seven-day rolling average is declining and sits at 15,565 compared with 17,020 last Tuesday. 

The reduction in case numbers was most pronounced in Auckland. More than 4000 cases were reported there last Monday and about 2300 yesterday. 

Canterbury and South Canterbury combined had a higher average than Auckland, and it had increased since last week. 

On Tuesday 842 people were in hospital across the country and 26 in ICU. 

Christchurch Hospital had had a slight increase in hospitalisations, with 63 of the 510 patients with Covid, McElnay said. 

Hospitalisations were expected to increase there this week. 

McElnay said she wouldn't describe Christchurch as the centre of the outbreak but it was experiencing a "peak". 

Meanwhile, it emerged yesterday that more than 200,000 school children have been staying home every day this month during the Omicron surge. 

Ministry of Education figures show more than 100,000 were learning from home on some days, while many others were sick with Covid-19. 

And modellers estimate as many as 1.7 million Kiwis have been exposed to Covid-19 during the pandemic. Scientists are still learning about whether we're at risk of reinfection with Omicron. 

One study estimates there is a 56 per cent effectiveness of natural immunity against Omicron from prior infection. 

Another has found booster shots have 76 per cent effectiveness at protecting Omicron-infected people against hospitalisation and death. 

- Julia Gabel and Michael Neilson, NZ Herald