Hollywood actor Arnold Schwarzenegger has hit out at Donald Trump over what the US president's critics say is a failure to unequivocally condemn white supremacists and bigotry following last weekend's violence in Charlottesville.

Schwarzenegger, who previously served as former Republican governor of California, said to Trump: "as president of this great country, you have a moral responsibility to send an unequivocal message that we don't stand for hate and racism."

In a video for media company ATTN, Schwarzenegger is then shown mockingly asking a miniature figure of Trump: "Was that that difficult?"