A visiting Malaysian family has been left distressed after their rental van was towed in what appears to be a parking scam in Melbourne's CBD.

The family of nine had parked the vehicle on Lonsdale Street last night only to return this morning to see it being towed.

Video obtained by 9News shows three workers, all dressed in hi-vis clothing, removing a black cover off the street sign to reveal a no parking zone.

A man in hi-vis seen taking the black cover hiding a parking sign. (9News)

In a statement to 9News, the City of Melbourne confirmed the "the individuals covering and uncovering the sign" were not its employees.

The council is currently investigating who the men are and why they covered the sign.