A public health expert fears 14,000 people in New Zealand could die from COVID-19 if the lockdown doesn't work.

The number of cases in New Zealand has risen to 647 today, and so far we've had one casualty.

Otago University's Professor Nick Wilson told Heather du-Plessis Allan extending the lockdown is one way to stop the virus spreading.

But he says it's an enormous cost to society, and the economy.

"So if we can do very intense testing and contact tracing, we can find all those cases and break all the lines of transmission." 

He says we might have to ramp up our measures even further if the lockdown isn't successful.