The group of around a dozen caravans and vehicles is understood to have arrived at Sandall Park earlier today, with the travellers believed to have illegally accessed the area.
Photos show vehicles on the old golf course of the park, now used as an exercise and dog walking area.
But the Free Press understands that the travellers have been ordered to leave the park tonight by Doncaster Council.
Coun Jane Kidd, Labour councillor for Wheatley Hills and Intake said: “I have just been in a meeting with council officers and concerning the gypsies on Sandall Park, to use their words, they are over it like a rash.”
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A separate camp has also been established on the former Benbow pub site on Armthorpe Road for most of this week.
She added: “The caravans on the Benbow site are proving problematic because the owner of the site is refusing to communicate with the Council. We are looking at different approaches to tackle the issue.”
Sandra Crabtree, chairman of Friends of Sandall Park said: “Parks are for recreation, exercise and play. They are not for traveller encampments.
"This is just so wrong in so many ways. Our volunteers put their heart and soul in to ensuring it is a fabulous place for families to enjoy outdoor space.
"It is a council owned park and we hope they resolve the situation quickly so it can once again be used for the purposes intended."
We have contacted South Yorkshire Police for a statement.