SYDNEY, April 10 - About 100 parents, students and activists gathered near Haberfield Public School on Tuesday morning to protest plans that would see two WestConnex construction sites on the school's doorstep.

One site would be used for tunnelling - with 140 heavy trucks attending daily - while a second would be used as a 150-space car park for workers.

Rachel Brittliff, who has a daughter at Haberfield Public School and a son in child care nearby, says existing construction already creates dust clouds that have sparked their asthma.

"We're already experiencing air pollution that's eight times the recommended amount," she said on Tuesday.

"It shouldn't be a consideration. We should be looking after constituents and residents - not large corporations."

Premier Gladys Berejiklian insists the government wouldn't be proceeding with the project unless everything had been done to minimise the impact of construction.

"Nothing is more important than the health of children, nothing is more important than making sure communities feel safe at all times, and that includes during major construction," she told reporters in Sydney.

"We've already laid down our plans for [stage three] and they're pretty clear.

"But if there is anything else we can do to mitigate the impact on the community we're always open-minded about that."