Melbourne Lord Mayor Robert Doyle has lashed out at vandals of a monument is Melbourne's CBD.

The Burke and Wills statue in City Square was found covered in political messages such as Vote one Wikileaks, Free Bradley Manning and End the police state.

Commericial cleaners will attempt to remove the wax crayon markings and it is hoped CCTV cameras may help identify the vandals.

Mr Doyle says vandalism only works to undermine political messages.

"What a mindless piece of vandalism," he said.

"The people who do this sort of thing surely do more harm to their cause than good.

"This doesn't publicise these groups. What it does is say they're prepared to thumb their nose at the rest of us."

Premier Denis Napthine has condemned the vandalism.

"I think that's absolutely disgraceful. That sort of vandalism is just stupid and people ought to know better," he said.