Police officers are standing guard at a cordon in a cemetery in Holbeck in Leeds.
The cordon is at the back of Holbeck cemetery this morning, close to the path on Beggar's Hill this morning.
A dog walker said she believed the 20m-wide cordon went up yesterday and said it has raised concerns after a woman was attacked earlier this summer .
She said: "I noticed it this morning while walking the dog. My neighbour saw it there yesterday evening. I think because of the 'managed approach' (to prostitution) the community is on tenterhooks.
"A lot of cordons go up and we never get answers. Every inch of parkland, open space and little corners get used and it is always on everybody's mind."
The Holbeck managed zone was introduced in 2014 and means that within the designated non-residential area, between the hours of 8pm and 6am, there will be no police prosecutions for soliciting or selling sex.
The managed zone has been heavily criticised with campaigners calling on the police and Leeds City Council to halt the scheme.
West Yorkshire Police has been asked for information.