Anyone arriving in the ACT from Victoria after 11.59pm Thursday must declare their travel with ACT Health, and can only leave their premises for essential reasons.

Those reasons include shopping for essentials such as groceries, essential work or study which can't be done remotely, for medical care, to get a COVID-19 vaccine or for exercise one hour per day.

People aged 12 and above must wear a mask when leaving for any of the allowed reasons, except for vigorous exercise.

No person can enter the ACT from Victoria without an exemption unless they are a resident.

Anyone who has been in Victoria from July 8 and left before midnight is required to complete an online declaration form, regardless of whether or not you they arrived arrived in the ACT.

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ACT Health has said "no travel to and from Victoria should take place at this time."

They said the new restrictions were likely to stay in place from 11.59pm Tuesday 20 July.

These rules are imposed when a state goes into lockdown to mirror those requirements.

Prior to the new order, there was a requirement for anyone who has travelled from greater Melbourne to complete an online declaration form and monitor for symptoms.

Earlier, Victorian Premier Dan Andrews announced with a "heavy heart" the state's fifth coronavirus lockdown on Thursday afternoon.

He said you only get one chance to go hard and fast.

"I am not prepared to avoid a five-day lockdown now only to find ourselves in a five-week or a five-month lockdown," the Premier said.

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