Travellers moved from Waterhall Golf Course appeared in Surrenden Park, Brighton, this morning.
A group of 11 caravans turned up at about 9am.
Terry Purcell posted this picture on Twitter earlier today.
The gate to the field was wide open, though the council says it was secured overnight.
Brighton and Hove City Council has confirmed the unauthorised encampment and has visited the site with the police to carry out a community impact assessment.
A spokeswoman for Brighton and Hove City Council said: "There was damage to the gate, so looks like a break in.
"The council’s traveller team has visited the site and is in discussion with the police on next steps."