A Palmerston North school has been forced to suspend all email services after the school system was hacked and a 'disturbing' message was sent to students.

Palmerston North Intermediate Normal School alerted parents to the hack on Sunday night. The disturbing email was sent to students' gmail accounts.

The school said it was taking the matter "extremely seriously". It has reported it to the police, and its IT specialists are working to track its origin.

At first the school suspended all gmail accounts after the hack, but it has now widened that to include all emails on the school system.

It is understood the email contained explicit sexual language.