South Australia is tightening some coronavirus measures with Premier Steven Marshall declaring the "entire nation is on high alert" amid the continuing surge in Melbourne cases.
From midnight on Tuesday, the state's hard border closure with Victoria will be extended to also prevent any South Australian residents returning home.
At the same time, SA will impose a 50-person cap on family gatherings and a 100-person cap for weddings and funerals.
Quarantine arrangements for people coming from NSW and the ACT will remain in place as concerns also remain over three COVID-19 clusters.
Victoria reported 300 new virus cases on Friday along with six more deaths and NSW another seven infections.
Mr Marshall said the new measures and reinforced arrangements were designed to prevent the "seeding" of virus infections into SA from other states.
"The entire nation is on high alert," the premier said on Friday.
"What we've seen in recent weeks, particularly in Victoria but also in NSW, give us real cause for concern.
"We want to be absolutely certain that we do everything that we can to protect the health of South Australians but also the economy."
SA's tougher restrictions will also include police taking a harder line with businesses not implementing a COVID-19 plan or not sticking to that plan.
Police Commissioner Grant Stevens said from Friday night any businesses found to be doing the wrong thing would be shut down, rather than just cautioned or fined.
He said the new approach would penalise those in breach of the regulations rather than whole business sectors.
SA has recorded three new coronavirus cases so far this week, with one of those, a man in his 40s, a wharf worker who had gone to Melbourne as an essential traveller.
His close contacts have also been tested for the virus with their results still to be returned.
But Chief Public Health Officer Nicola Spurrier said the man's wife and a friend work in two of Adelaide's hospitals, the Queen Elizabeth and the Royal Adelaide, so about 10 hospital staff have been sent home as a precaution.
The man's case took the state's total COVID-19 infections to 447 since the start of the pandemic.
It has prompted changes to some measures for essential travellers with truck drivers bringing freight across the borders now to be tested every seven days.