Ex-Prime Minister Sir John Key has raised questions about how New Zealand leaves the coronavirus Level 4 Alert, saying it will be "challenging" for this country to exit that.

Talking on Mike Hosking Breakfast on Newstalk ZB, Key raised the spectre of the practicality of the country moving out of this phase.

"It's easier to get into lockdown. It's much harder to get out. What does it mean - go back to Level 3?" he asked.

"That's going to be the challenge - how you get out of this thing."

He referred to restaurants and potential confusion of when they could open and when they must shut and raised questions about moving from Level 4 to Level 3 and Level 2.

If New Zealand was five weeks behind Italy in terms of coronavirus cases and three weeks behind the United States, why in three weeks "would we return to normality? If we go from Level 4 to Level 2 and then we go back to Level 3 again, what does that mean for business that might start up? You're a restaurant, you're at Level 2, you're back operating again. Oh, now you're at Level 3. You can't. That's going to be the challenge I think here is how we get out of this thing."

The entry point into lockdown was not easy "but conceptually it's easier to get into lockdown. It's much harder to work out how to get out of lockdown."

He also hinted at the possibility of the lockdown lasting longer than the initial planned month.

Asked about the four weeks and if he expected the Government would stick to that, Key said: "I reckon they simply just don't know. I reckon nobody knows. I mean if you look at the United States and New York's a basket case and they've been talking 90-day lockdown from the get-go and then you look at Australia - it strikes me any country that has a federal and state governments and in the United States you've got that and in Australia, they have real problems because a lot of the states run the hospital systems and run the schools."

Key said that a few weeks ago, it would have been difficult for New Zealanders to imagine what life would become like now "and I think we all would have looked at each other and thought that's pretty odd and not going to happen".

Yet now New Zealanders were surviving through the Level 4 alert and people could understand it, he said. Sometimes it was difficult for politicians who might be ahead of the rest of the population. But if they made decisions too early, they had a problem carrying public support.

Australian PM Scott Morrison "looks like he might be lagging a bit" but Key said it was hard to know.

The Government had to be a big part of recovery, he said, citing the Reserve Bank and working with the banks on working capital, taking the brunt of the risk to customers, "because enough loans wouldn't be made" without that.

"The reality is you need the Government doing this. A third of people probably still are working in some sort of emergency capacity. About a third of people were working from home but probably on much lower levels of productivity" and the final third were not working, Key said.

"So that's a massive chunk of economic activity. How do you get that going again? That's going to require confidence." He cited the global financial crisis and the job summit under National "and out of that came some ideas. Some of those worked and we put them into practice but some of them didn't work".

The job summit bringing employers, unions, the Government and others together in one place was another practical result from the GFC, Key said, hinting that an event like that could help economic activity recover.

People "would have to park their ideology up at the door when you have those discussions." He cited small businesses struggling and taking the job subsidy: "Do you really need to drown those people in red tape and bureaucracy? I think we're going to have to look to lighten the load on them and let business start to flourish a bit. These aren't normal times."

• Covid19.govt.nz: The Government's official Covid-19 advisory website