NSW residents are being urged to use their common sense to decide for themselves if they are essential workers as the state struggles with a COVID-19 outbreak.

NSW has baulked at defining "essential work" during Sydney's COVID-19 lockdown with workers urged to use their "common sense" to determine who can and can't leave home.

"It is so, so difficult to have a precise rule for every single thing," Premier Gladys Berejiklian told reporters on Tuesday.

"That's why we rely on common sense (and why) we rely on people to respect the intent of the health orders as well as the letter of the health orders."

One of the 89 new cases reported on Tuesday in NSW was a Sydney painter who left lockdown to work on a hospital construction site in Goulburn, 200km southwest of Sydney.

Goulburn Mayor Bob Kirk fears the loose definition of "essential work" is putting regional towns at risk.

"The COVID disease doesn't ask people if they have a travel exemption or not, it just attaches to whoever it can," he told AAP on Tuesday.

"But I understand he is a painter ... I don't know how that qualifies as essential right now."

"I know there are more than a few painters around this place that could step up if needed."

Fairfield in Sydney's southwest remains a focal point of restrictions, with a new public health order aimed at shaking out unknown cases.

From Wednesday, people leaving or entering the Fairfield local government area for essential work will need to carry proof they've had a COVID test in the past three days.

"Don't go outside the Fairfield local government area, even if you consider your work is essential, rethink that," Health Minister Brad Hazzard said.

"But if it really is essential, you must have a test every three days."

Those leaving Greater Sydney will need to carry evidence they've had a test in the past seven days.

Mr Hazzard rebuffed suggestions the government should define "essential work" to provide clarity, saying creating a definition was challenging and people would always find loopholes.

Bosses and their workers know whether each worker is essential, he said.

"So it will be left to the worker and to the employer," he said.

"But my message - to the employers particularly - is if you don't need to have someone come from an area that is suspect and obviously has major COVID concerns presently, then perhaps it might be an idea to make arrangements for a worker from another area."

Under the restrictions, essential workers can take their children to school.

Schools trying to work out which parents were essential workers should look at what NSW did last time it was in lockdown, Ms Berejiklian said.

"There are very vulnerable children, children in very special circumstances which require that attendance," she said.