A bag filled with human excrement has been thrown at a bus driver in Melbourne's north before exploding over his face, hitting his eye and splattering across his driver's seat.

The bus driver stopped to let a passenger off in Wollert at 9.40pm on November 13 when a bearded Caucasian man, aged 30 to 40, stepped onto the bus.

Police say this man threw a bag of faeces at a bus driver. Credit:Police Media

The high-vis-clad man lobbed a plastic bag of poo at the driver before running off.

"Obviously the faeces has gone all over the driver," acting Sergeant Todd Little told reporters on Monday.