The school told families via social media that NSW Fire and Rescue had given the 'all clear' and students had been sent to recess and then to period four classes.

As reported earlier, students were evacuated to the back oval after the gas leak and then to the hall, which had been cleared as safe.

Parents had been asked not to attend to pick up their children.

A Department of Education spokesperson said all students and staff were evacuated to the school's assembly point on its playing fields "as part of standard school procedures" after gas was smelt across the school about 10.20am.

"Emergency services were contacted immediately by the school," the spokesperson said.

"Emergency services then confirmed the source of the smell was not on the grounds and gave a full clearance for all students and staff to access all school facilities.

"The school safely resumed normal operations at 11.40am."

PARENTS of students at Hunter School of the Performing Arts have been advised not to attend to pick up their evacuated children.

Students were evacuated to the back oval after a gas leak at the school and have since been moved to the hall, which has been cleared by NSW Fire and Rescue as safe.

The Department of Education has been contacted for comment.

More to come.