For the first time in more than a year, a person has tested positive to COVID-19 and was infectious in the community for four days.

Three close contacts of that man have tested positive, while the source of the infection remains unknown.

"We have one opportunity to stamp this out," Mr Barr said.

"We all have a collective responsibility to each other. To make sure we are successful."

It is the first time Canberrans have been sent into lockdown since the initial nationwide lockdown in 2020.

Here's everything we know about the ACT's second lockdown.

Some of the essential reasons to leave during lockdown:

A more detailed breakdown of reasons to leave is available on the ACT COVID-19 website.

"Stay within your local area," Mr Barr said.

"If you live in Belconnen, exercise in Belconnen. Get your groceries and essential supplies in Belconnnen."

Travel for essential reasons such as healthcare or vaccination outside of your region is acceptable.

All family gatherings are banned. People should only be interacting with other people in their household.

Two people are permitted to gather for exercise.

Mask wearing will be mandatory in the ACT for anyone aged over 12 years of age, whenever they leave their house.

The only exception is when doing vigorous exercise.

Canberrans will also be required to maintain good hand hygiene and keep their distance from others.

People are still required to use the Check in CBR app when entering essential locations, and are reminded of the critical need to do so.

Public school families have been directed to access home learning resources online next week, with no teacher-led remote learning.

Schools, before- and after-school care and childcare providers will remain open for children of essential workers or for students in vulnerable circumstances.

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"If you are an essential worker, if you are experiencing vulnerability, or if for some other reason you can't keep your children at home, then your children can still attend the local public school," ACT Education Minister Yvette Berry said on Thursday.

"Public school teachers will spend this period of time moving and planning for and transitioning to remote education, should they be required after this initial lockdown period."

Independent schools will start remote learning on Monday.

Catholic systemic schools will begin remote learning on Tuesday.

The lockdown has been announced for seven days, starting from Thursday at 5pm.

Essential businesses which will remain open include supermarkets, chemists, post offices, hardware stores, mechanics, banks, bottleshops, locksmiths, petrol stations, laundromats and newsagents.

General retail will be closed, and hospitality venues will only be allowed to operate takeaway services.

"What we need is people to come in get what they need and leave," Mr Barr said.

All nightclubs and licensed venues must close but can trade as off-licensed venues.

Religious gatherings must move to livestreamed services.

No more than 10 people can attend a funeral, excluding the people conducting the service.

No more than five people can attend a wedding, including the people getting married, a celebrant and two witnesses.

All gyms must close, and personal training, bootcamps, dance classes and all community sport, including training, cannot go ahead.

Swimming pools are closed but hydrotherapy pools can remain open.

Outdoor playgrounds and nature reserves are closed to the public.

Visitors to aged care facilities, hospitals or health settings are banned with some exceptions, including end-of-life reasons, support partners for births, adults accompanying a child or for compassionate reasons which must be approved by the facility.

Residents of Canberra's surrounding regions will be given a standing exemption to enter the territory for essential purposes, as police prepare to ramp up border checks.

People who live across the border in communities including Queanbeyan, Jerrabomberra, Gundaroo, Yass, Murrumbateman and Collector will be able to enter Canberra to attend essential work or for other essential reasons such as groceries or healthcare.

NSW residents outside of the exempted regions must apply for and receive an approved exemption to enter the ACT.

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