A number of caravans and vehicles arrived at the large grassed area between Anscombe Road and Bernard Road at around 2.30pm.
Worthing Borough Council has informed Sussex Police.
Council leader Paul Yallop said previous encampments had caused stress to vulnerable residents in his ward and he hoped police would deal with the situation.
He said: “The police will need to consider the community impact and possible use of powers to direct the travellers off the site.
“I have some vulnerable residents who are very stressed by these repeated incursions. I hope the police will consider the health and well being of my residents when making their decision.
“One retired gentleman was found unconscious on his living room floor last summer due to the stress of the situation.”
He added: “If the police will not use their powers the council will be following standard procedures but the holiday weekend will delay that process.”
The council took action to build the bund and barrier after two illegal encampments last summer.
In one incident, residents, including former councillor Tom Wye, used their cars to block off the area.