Entry into Mary Street from Beaufort Street will be blocked off from Friday, allowing traffic to exit only into Beaufort Street.
It is part of a two-week trial in Highgate, to transform the hub into a meeting place.
Mr Carey said the piazza would provide needed public open space for Beaufort Street.
‘We are trying to help the community imagine how this piazza could really be,’ he said.
‘Rather than going out with the design on paper, what we are doing is creating a trial of what could be there, asking for people’s views and opinions and then help them formulate a final plan.’
Costing about $180,000, the piazza will have fake grass, seating, temporary plants and blackboards people can write on.
Throughout the trial, yoga, face painting, balloon making, a school produce market, buskers and art will also bring life to the street.
Mr Carey said restricting traffic flow through part of Mary Street would help make the streets safer for pedestrians and cyclists.
‘If you prioritise town centres for people and cyclists then you create more activity because people want to stay there.’
The trial will run until Friday, August 8, and there will be a community forum at 10am on August 2. If positive feedback is received, it could become a permanent feature.