The group, calling itself Westbury Region Against the Prison, incorporated on Saturday, following a rally attended by hundreds of people at the Town Hall.

Passionate views on the prison proposal were exchanged at the rally, and the atmosphere grew heated when Lyons Liberal MHAs Mark Shelton and John Tucker addressed the crowd.

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WRAP organiser Heather Donaldson said the group had been "strongly encouraged" by the public support shown at the rally.

"We had to change plans at the last minute and shift the rally [from the Village Green] to the Town Hall because of the weather," Ms Donaldson said. "It's lucky we had booked the larger hall, as it was filled to overflowing."

"We were overwhelmed by the level of attendance and support shown by the community for this event."

Ms Donaldson said a key message to come out of the rally was that many locals wanted the state government to reveal the other nine sites that had been considered for the prison.

WRAP is expected to hold its first committee meeting on Thursday.

Corrections Minister Elise Archer said an "important personal commitment" meant she had been unable to attend the rally on the weekend.

"It is and always has been my intention to visit Westbury and hear directly from residents and business owners about the preferred site for the Northern Regional Prison," she said.