Police are hunting a man who performed naked chin-ups in front of two young girls at a Kilsyth school on Sunday.

Investigators have been told two girls, aged 10 and 11, were riding their bikes on the school grounds on Mount Dandenong Road about 2.45pm.

The man was seen loitering in the area before removing all of his clothing and proceeding to do chin-ups on the monkey bars.

He is believed to be aged between 25 and 30 and is approximately 175cm tall with dark hair that is short at the back and spiked on top.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or visit www.crimestoppersvic.com.au.