As of 12.01am on Tuesday, interstate visitors are allowed to enter South Australia provided they are fully vaccinated and have applied through the EntryCheckSA process.

Quarantine requirements depend on where a person has arrived from. International visitors or domestic arrivals from areas deemed "high risk" will need to quarantine for seven days.

Most interstate arrivals will need to take a COVID-19 test in the 72 hours prior to arriving in South Australia.

Premier Steven Marshall said the state had been working on becoming COVID-ready for "months".

"A lot of people have been waiting for this day. They've been dislocated from friends and family and of course they've been dislocated from business opportunities," Mr Marshall said.

South Australia's current double-dose vaccination rate is 77.4 per cent, shy of the anticipated 80 per cent target to open state borders.

Police reinforcements have been sent to the state's land borders, as authorities expect hundreds of residents to enter the state via road after midnight.