Travellers with 16 vehicles have reportedly moved onto Tangmere Airfield.
According to Andrew Irwin, chairman of Tangmere Parish Council, the 16 vehicles arrived on Tuesday afternoon after gaining access to the site via Fulmar Way.
He believed that West Sussex County Council was aware of the situation.
According to the chairman, the travellers had previously been moved on from The Angmering School in Angmering, where they had pitched up on the school fields on its sports day. This has not been confirmed by the authorities.
Mr Irwin said he was 'disappointed there was not any intelligence passed on that there was an impending eviction'.
He added: "We are doubling our efforts to make sure our recreation field in Malcolm Road is secure."
A Sussex Police spokesman said it had records of an incident last night (Friday, July 12) at the site but could not comment further.
The county council has also been approached for comment.