Demountables have been placed on teacher car parks and new classrooms created within schools to cope with rising student numbers at increasingly popular public schools, the department has confirmed.

Enrolments at some public schools this year are up by as much as 13 per cent on 2012, according to draft figures collected by the Northern Sydney Regional Council of Parents and Citizens Associations.

Enrolments at Greenwich Public School rose by 13.4 per cent on 2012, at Mowbray Public School by 9.5 per cent and at Cammeray Public School by 9 per cent, according to the council. Primary school enrolments across the area rose by an average of 5.5 per cent.

''One school requested that demountable buildings be located on a car park to ensure that play space was maintained. Alternative parking arrangements for staff are in place,'' a department spokeswoman said.

The department also confirmed it has had to create new classrooms within several schools.

The council and the Department of Education and Communities are negotiating selling or leasing the former Anzac Memorial Club site in Cammeray for use as a primary school. The mayor of North Sydney, Jilly Gibson, said she hoped to reach an agreement soon, subject to an updated evaluation.

The enrolments data was collected in week one of term and may change as enrolments are finalised.

Enrolments at Mosman High School rose 9.9 per cent to 975 this year, according to the Northern Sydney Regional Council of Parents and Citizens Associations.

The president of Mosman's P&C, Celia Harper, said urgent action was required. ''Because of our very small site we either need a multi-storey building or for the [department] to open a new high school in our area,'' she said.

Parents from a number of P&Cs have also expressed concern about the impact of the proposed $200 million redevelopment of the Channel Nine site at Willoughby, which would contain 663 new dwellings.