The outbreak - linked to the Holiday Inn at Melbourne Airport - has grown to 13 cases, with Victoria set to go into a five-day lockdown from 11.59pm on Friday.

Premier Steven Marshall said the border restrictions would affect all travellers from Victoria - including cross-border communities - for the five days.

"We understand this is going to have a massive effect on people lives but our primary concern is keeping South Australia safe," he told reporters.

"We are concerned about the unfolding situation in Victoria that's why we moved promptly. Our thoughts are with our friends across the border."

The health directive takes effect from midnight on Friday.

Anyone who travels through Tullamarine Airport will now be required to quarantine for 14 days.

People in SA who were in Terminal 4 of the airport from February 9 will also have to quarantine for 14 days from the date they arrived.

Family and household contacts must also get tested and isolate until they receive a negative result.

Anyone who was at the airport - including airline staff, their family and household contacts - from February 7 must get tested and isolate until they receive a negative result.

"I really want to thank every single person in South Australia for their patience and working with the restrictions," Mr Marshall said.

"I know they are inconvenient but by working together we can stay safe and keep the economy strong."

Chief Public Health Officer Nicola Spurrier said the situation in Victoria was progressing rapidly.

"This is a variant of concern. It is the UK B117 strain of COVID and it seems to be moving very rapidly and we are seeing increasing numbers."

Professor Spurrier said two contacts of cases linked to the Melbourne Airport Holiday Inn had worked at Tullamarine airport while infected.

One was a cafe worker at Terminal four, which services passengers flying with JetStar and Rex Airlines.

The other worker was a cleaner who went to a larger number of areas, which are now considered potential exposure sites, Prof Spurrier said.

Victorian authorities are working to track down 5000 people who passed through the terminal on February 9 between 4.45am and 1.15pm.

About 29 flights arrived and departed through the terminal during the eight-hour window.

The outbreak can be traced back to a family of three who quarantined at the Holiday Inn and are believed to have been infected overseas.

There were no new COVID-19 cases diagnosed in SA on Friday. There are five active cases in the quarantine hotels.

Australian Associated Press