Vandals have illegally chopped down five 100-year-old native trees in Lerderderg State Park, about 30 kilometres north-west of Melbourne.

A chainsaw was used to fell the trees, which were at the perimeter of a new campsite at the reserve, between December 3 and December 4.

One of the trees that was felled at the Lerderderg State Park. Credit:Victoria Police

Parks Victoria district manager Tony English said the trees were stringybarks and grey-gums, some of which were more than 100 years old.

"We see a lot of things going on in our parks, but this is a senseless act we are struggling to understand," he told radio station 3AW.