Police were informed after the student told teachers how he was grabbed on the arm by a man in the toilets of Mandama Primary School in Grovedale just before 2pm on Tuesday.

The boy was able to break free after punching the man and running away, police said.

"The boy has notified teachers who reported the matter to police," police spokeswoman Leonie Johnson said.

"Police conducted a patrol of the area but were unable to locate the man."

The man is described as Caucasian, aged between 20-30, tall, with a skinny build and dark stubble.

He was wearing a black hoodie with the hood up and black sunglasses. Police said he was last seen leaving the school grounds on foot towards Corang Avenue.

Department of Education spokesman Steve Tolley said the incident was being taken seriously and staff would continue to work closely with the police.

"A student at Mandama Primary School today reported to teachers that he had been approached by a man on school grounds," he said.

"The child is safe and the safety of our students is our number one priority"

Mr Tolley said the school had contacted the police who spoke to the child and their family about the incident.

"The Department will also work closely with the school and provide any support required," he said.

Anyone with any information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report to www.crimestoppersvic.com.au