Covid-19 cases have risen since last week as experts warn New Zealand's pandemic model is out of date.

There have been 1248 new cases of Covid-19 reported in New Zealand over the week to Sunday, and 12 further deaths attributed to the virus.

There were 77 cases in hospital.

The update comes as the Auditor-General warned the government the Ministry of Health was relying on modelling that was nearly 20 years out of date, and there was a risk New Zealand would not have enough antiviral or vaccine supplies if another pandemic were to strike.

Last week, controller and Auditor-General John Ryan said there had been patchy progress on implementing recommendations made by his office in 2020, when Covid-19 exposed major gaps in the country's preparedness.

The health system was "better positioned" than it was five years ago to source, manage, and distribute personal protective equipment because these functions had been centralised in Health New Zealand / Te Whatu Ora, he wrote.

"However, progress has not been consistent across all of our recommendations, including the need to update national plans and modelling to determine how much stock should be held in the NRS [national reserve stocks] and who should have access to it."

Last week, Te Whatu Ora reported 889 new cases and seven further deaths.