Around 25 caravans and vans have moved onto land in Rushey Platt.
Wiltshire Police said officers were aware of the camp on Scott Way, between Rushey Platt and the Mannington retail park. The vehicles had moved onto the land on Thursday evening.
A force spokesman said: "We are currently making patrols in the area while the group remains.
"We appreciate the public’s patience while this matter is progressed and would urge anyone to call us if there is any anti-social behaviour or disorder caused."
In May, caravans moved onto a field between Mannington retail park and Redposts Drive.
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