ACT Policing have set up a COVID-19 checkpoint on the Barton Highway near Hall.
There are reports of significant traffic delays on the highway.
Chief police officer for the ACT Neil Gaughan said on Wednesday border checkpoints worked as a deterrent to people who should not enter the ACT.
"We're obviously not there 24/7... we're obviously not saying when we are opening and closing those check points," he said.
"The fact we stopped 16 people [on Tuesday] coming into the territory I think does show [COVID-19 checkpoints] have been quite effective.
"There's been over 170 vehicles that we've turned around since the weekend."
Chief officer Gaughan encouraged Canberrans to use appropriate channels to inform police if they were aware of people in the ACT who should not be in territory.
"If we find people from Greater Sydney area we will be fining them $8000," he said.
The chief police officer defended the scale of the border checkpoint operation.
"If we look at what's occurring across world and across Australia with coronavirus, I think it is appropriate to allocate significant resources to the health direction," he said.
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