A volunteer directs a resident at a Covid-19 drive-through testing clinic in eastern Brisbane on Saturday. AFP

Australia's third-largest city of Brisbane and eleven Queensland local government areas will enter a snap coronavirus lockdown from Saturday.

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Authorities race to contain an emerging outbreak of the Delta strain as millions of residents in the city and several other areas will be placed under stay-at-home orders from Saturday afternoon for three days.

Residents queue up outside a shopping centre in Brisbane on Saturday. AFP

"The only way to beat the Delta strain is to move quickly, to be fast and to be strong," state Deputy Premier Steven Miles said.

An estimated population of 3,288,000, have now gone into a three-day lockdown, after seven new local cases of Covid-19 — all the highly infectious Delta strain — were recorded.

There were now seven cases of the Delta strain of the coronavirus in Queensland mainly linked to a school student, her family and a tutor, but authorities were still trying to trace the source of the outbreak, Miles said.

Volunteers direct traffic at a Covid-19 drive-through testing clinic in Brisbane on Saturday. AFP

In the "strictest lockdown" the city has enforced, residents will only be allowed to leave their homes for essential reasons including buying groceries and exercising.

Brisbane's snap lockdown comes as Australia's largest city of Sydney and its surroundings completed its fifth week of lockdown with authorities struggling to stop the spread of a Delta-variant outbreak.

"We cannot afford to be complacent just because we have done so well so far. We all we have to comply with these restrictions," Miles said.