Air New Zealand is pleading with no show customers to cancel bookings so their seats can be grabbed by desperate Kiwis trying to get home before tomorrow night's lockdown.

Thousands of New Zealanders stranded around the country are in a desperate race against time to get home before sweeping measures to prevent the spread of Covid-19 come into force at 11.59pm on Wednesday.

They are set to choke airports amid a scramble for last minute flights.

The country's national carrier says it is adding extra capacity to the network including putting on wide body jets on some domestic routes.

Air New Zealand is also pleading for "no show" customers to cancel their flights to free up seats for those Kiwis who are desperately trying to reach loved ones before the window of opportunity closes.

"This will allow New Zealanders seeking to return home to do so prior to the country moving to alert level four," an airline spokesman said

The Government announced yesterday that New Zealanders would be forced into four weeks of self-isolation from 11.59pm on Wednesday in an attempt to stop the deadly spread of Covid19.

The unprecedented measures include limiting all non-essential domestic travel and a complete shut down of all non-essential services like restaurants, bars, cafes, gyms, movie theatres and libraries.

Prime Minister Jacinda Ardern urged Kiwis to "go home", telling citizens if they were in a different part of the country they should make immediate arrangements to return.

One Kiwi traveller trying to depart Christchurch wrote: "Thousands of people at the Chch airport waiting in lines, violating distance rules, only to be told; 'I can't help you'. No planes are flying but Govt says 'get home'. Yea right! We are scheduled to fly on Thursday. We're praying for some kind of response from Air NZ."

Despite Air NZ's plea for customers not intending to fly to cancel their bookings, this is proving difficult for some air travellers.

Dave Greenberg wrote on Twitter: I tried to cancel my flights today, but couldn't manage via app because it was through govt dept travel agent. Understandably Couldn't get through to them or Air NZ call centre. Any way to let the apps take a cancel no matter how booked?"

Another woman was desperate for information on how her children could get home.

"Can you please advise if my young people will be permitted to fly home from uni - Dunedin to Wellington on Friday on already booked flights?"

Though the lockdown comes into force at midnight tomorrow, the Government has indicated there will be allowances for people not able to meet the deadline. Anyone who is unsure should call the Covid-19 information helpline on 0800 779 997 to let them know your circumstances and get advice.

Auckland Airports website has the following information for travellers:

"Passengers can still fly domestically until the Government's Covid-19 alert status shifts to Level 4, at 11.59pm on Wednesday.

"After this point, only travel undertaken for essential services will be permitted for domestic flights.

"Passengers are directed to contact their airline for details on whether their journey fits this description. Domestic flights for freight will also continue."

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