Travellers set up camp outside a former food distribution warehouse this week.
About 10 caravans and panel vans turned up at the site on Warneford Avenue, in the Street Side area, on Tuesday.
And Wakefield Council is powerless to move the travellers because they are on a private car park.
People living on the street said they could hear the constant sound of a generator rumbling.
They said they did not know who currently owned the site, but said it used to be a distribution warehouse and was being refurbished a few months ago.
Acting inspector Mark Chamberlain, of the northwest neighbourhood police team, said: “We are making enquiries into the ownership of the land and will advise the landowner of the occupation.
“In the first instance, it is the landowner’s responsibility to make requests for them to leave.
“Then, if certain criteria are met, and the trespassers have refused to leave within a reasonable time, the police can take action and assist in the removal.
“In this case at this time, there has been dialogue between officers and the travellers and some have left already.
“The situation will be monitored by the police.”
Neighbours said some travellers had recently set up at a former bacon factory on the same road, near to its junction with Dewsbury Road.
And a group also turned up on Ossett Common Rovers’ pitch at Illingworth Park several years ago.
Wakefield Council’s cabinet committee said at the end of last year that there was a shortage of sites for travellers in the area, and that they needed to create another seven pitches to deal with demand over the next five years.
But the council’s attempts to allocate land for travellers’ sites have caused a great deal of opposition.
In 2010, a public meeting was held in Ossett Town Hall over plans to build a site in place of the waste tip on Owl Lane.
But the meeting was overrun by hundreds of protesters, who later organised a protest march from Shaw Cross to Ossett town centre to show the strength of feeling.
The council eventually changed its mind and scrapped the proposal from its Local Development Framework (LDF).