Protesters camped in Hindmarsh Square will be forcibly removed if they have not left the site by Tuesday afternoon, the Adelaide City Council says.

About 25 Occupy Adelaide protesters set up a dozen tents on Saturday.

Lord Mayor Stephen Yarwood spoke to the protesters on Monday afternoon before council staff gave them a deadline to leave.

The council's chief executive Peter Smith says the group has until 3:00pm on Tuesday to pack up.

"We just have a simple by-law, which is by-law Three, which prohibits people setting up camp or tents in the city's parks or squares," he said.

"Generally in these situations we try and say to people, 'Look, without discussion of your right to protest and all those things, our main interest is upholding the law'."

The group is part of the global Occupy movement which started in New York as a protest against corporate greed.

The group says it is peacefully demonstrating against social injustice in the interest of profit.

One of the group, Sean, says he is standing up for what he believes in.

"I think it's very important to recognise that something is fundamentally wrong with our economic and political system and people here want to see something change, they want to at least provide a forum where ordinary people can talk about problems that society has, outside of the parliamentary system," he said.