Lockdowns in SA and Victoria: What you need to know about COVID-19 in Australia today.

- With AAP. 

Australia will have three states in lockdown for at least the next week, as the Delta variant of COVID-19 has spread via community transmission around NSW, Victoria and South Australia. 

On Tuesday, South Australia Premier Steven Marshall announced a snap seven-day lockdown from 6pm this evening, whilst Victoria has extended their lockdown for another seven days. 

Here's everything you need to know about the latest updates on the COVID-19 pandemic today. 

South Australia enters snap lockdown after five cases.

South Australia will move into a full seven-day lockdown on Tuesday afternoon after a cluster of COVID-19 cases grew to five.

The lockdown rules will come into effect from 6pm tonight, with South Australians only allowed out to leave for essential care, essential work, the purchase of foods and essential goods, for medical reasons and for limited exercise.

The fifth case is someone who dined at a restaurant in Adelaide where previously infected people were also present on Saturday night. The current cases are the Delta variant of the disease.

"We hate putting these restrictions in place but we have one chance to get this right," South Australian Premier Steven Marshall said on Tuesday morning.

"We are moving as quickly as we can to slow and stop the spread of this cluster.

"We know these restrictions will take a heavy toll. But we've always had a situation where we go hard and we go early in South Australia.

"We've got to stop movement around this state and we've got to stop it immediately."

The SA cluster began with an 81-year-old man who entered the country from Argentina, his daughter and another two men.

The elderly man had returned to Australia via NSW, where he spent 14 days in quarantine.

He returned to South Australia on July 8 and presented to a suburban hospital over the weekend after developing symptoms.

Victoria extends lockdown by seven days. 

Victoria's lockdown will be extended by seven days. Image: Getty. 

Victoria will stay in lockdown until at least July 27, as it records 13 new locally acquired cases of coronavirus.

Victorian Premier Daniel Andrews confirmed the lockdown extension of at least seven days on Tuesday, hours before it was originally flagged to end.

Of the 13 new local infections, four were previously announced by authorities and one is unlinked to a current cluster or outbreak.

"As promising as our progress has been, avoiding a New South Wales-style long, lengthy, very challenging lockdown where you just lose control of cases, we have avoided that," Mr Andrews told reporters.

"But, we need more time. That is why on the advice of the chief health officer we will extend these lockdowns for a further seven days.

"So far, the strategy is unfolding exactly the way that we would like it to unfold, but we have had a couple of super spreader events."

Almost a third of Victoria's locally acquired coronavirus cases can be traced back to a sports fan who attended an AFL match, a Euro 2020 viewing party and the rugby while unknowingly infectious.

That man caught the virus from a resident of a Maribyrnong apartment complex who caught the virus from unmasked NSW removalists and went on to spread it to friends and family.

Twelve of Tuesday's cases are linked to the current outbreaks of the Delta variant in the state, which originated in NSW, while one case remains under investigation.

Nine of the cases were in isolation during their infectious period.

NSW records 78 new cases.

NSW police officers patrol the Bondi Beach boardwalk during lockdown. Image: Getty.

NSW has recorded 78 new local COVID cases as people in Greater Sydney continue to live under the state's strictest stay-at-home orders since the pandemic began.

Of the new cases diagnosed from 62,860 tests in the 24-hours until 8pm on Monday, at least 38 were circulating in the community for some or all of their infectious period.

The 78 new cases is down on the 98 reported on the previous day.

NSW Premier Gladys Berejiklian said the efforts of the community was making a difference.

"That 78 number would have been much, much higher had people not been doing the right thing," the premier said on Tuesday.

A total of 1418 people have been diagnosed with the virus since the outbreak began on June 16.

People living in Greater Sydney, Blue Mountains, Central Coast, Wollongong, and Shellharbour are in the fourth week of a lockdown and the government is under intense pressure over a sudden decision to shut down the state's construction industry.

Builders, unions and constriction companies have formed a united front to lobby the government to allow some workers back on sites before the end of the month.

Feature image: Getty.