Less than 24 hours after 12 New Zealand visitors arrived into South Australia, the state has announced they will open their borders to travellers from across the ditch effective immediately.

Police Commissioner Grant Stevens said the backflip meant the state would welcome direct flights from New Zealand, joining neighbouring Northern Territory and NSW in the country's trans-Tasman travel bubble.

"I'm pleased to be able to announce with New Zealand people arriving in SA, they will no longer be required to quarantine," he said.

"We're also happy to receive direct flights from New Zealand.

"The current arrangements are that all 12 people we have in quarantine in SA have travelled directly from NZ to SA, only transiting through Sydney, so on that basis, direct flights from NZ would be within those arrangements."

Stevens said the state now felt comfortable with allowing the international arrivals into the state, saying he and the state's Premier Steven Marshall have no regrets on taking precautionary measures.

"We hadn't had specific advice in relation to the status of COVID-19 in New Zealand (when the travellers arrived)," Commissioner Stevens said.

"The health advice has been assessed by direct communication through our chief public health officer with New Zealand authorities and there is a level of comfort there in terms of the extent of COVID-19 that allows us to make this decision."

On Monday, five travellers from New Zealand arrived in Adelaide after passing through other airports from New Zealand.

All of the travellers were put into hotel quarantine, Mr Marshall told reporters, but they have since been released given the new travel advisory.

"We don't apologise for taking steps to ensure the safety of the South Australian community," Commissioner Stevens said.

"These people will have been inconvenienced for a relatively short period of time, while we made a proper assessment of the risk to South Australia."

New Zealand residents began arriving into Australia on Friday, with three plane-loads of passengers touching down in Sydney from midday.