The rules of Greater Brisbane's snap three-day lockdown will be the same as January's lockdown, with just four valid reasons to leave home.

Residents will be allowed to undertake essential work, buy essential supplies such as food and medicine, look after vulnerable people and exercise with members of their household or one other person.

A maximum of two visitors are allowed in people's homes.

Masks will be mandatory from 5pm on Monday, aside from those with a medical exemption, and schools will be closed except to the children of essential workers.

Anyone who has been in the Greater Brisbane area since March 20 is subject to the same restrictions regardless of where they live.

The region encompasses the council areas of Brisbane, Logan, Ipswich, Moreton Bay and Redlands.

Four new cases of community transmission were announced on Monday, and the measures are in place to allow authorities to work through the venues visited and identify potential contacts.

The cases include two work colleagues of one of the two original cases in the new cluster as well as a nurse who worked in a COVID ward and her sister.

Genome sequencing results due late tonight or tomorrow morning should clarify if the nurse acquired the virus at work.

One of the new cases travelled to Gladstone in central Queensland while infectious, and two travelled to Byron Bay.

The rest of Queensland is also subject to new restrictions given the opportunity for the virus to spread since the new cases have been infectious in the community.

Gatherings in people's homes will be limited to 30 people, dining and drinking will be sit-down only, and visitation will be cut at aged care facilities, hospitals and prisons.

Chief Health Officer Jeannette Young also asked those outside Greater Brisbane to wear a mask when they're inside a public venue and physical distancing isn't possible.

There is not a requirement to wear a mask when outside for people outside Greater Brisbane.

Greater Brisbane has been declared a hotspot, and Premier Annastacia Palaszczuk has advised other states and territories to do the same.