An estimated $30,000 worth of damage has been caused to the King Edward Park in an act of "senseless vandalism".
Ornate fencing on the 126-year-old structure Victorian rotunda was knocked out of the structure onto the grass.
A NSW police spokesperson said the malicious damage occurred between 6pm Sunday and 7am Monday and was being investigated.
Friends of King Edward Park president Louisa Connors said the destruction was "a really sad thing".
"The park is a fantastic resource for so many people," she said.
"To have it damaged in this way is pretty disappointing.
"The rotunda is a really integral part of the park.
"It's a terrible thing that didn't need to happen."
City of Newcastle said it was "incredible disappointing to see the senseless vandalism", asking the simple question: "why?"
"City of Newcastle strongly condemns this activity, as it not only damages much-loved shared community spaces, but is dangerous and costly to repair," a council spokesperson said.
"City of Newcastle has installed temporary fencing around the rotunda to keep the community safe while materials are sourced and remediation works undertaken which will take place as soon as possible."
The council is working to ensure any users that had booked to use the area were aware of the situation.
The rotunda was built in 1898 by local carpenter Thomas Hardman after the Newcastle Borough Council called for tenders, according to the National Trust.
It was restored in the 1960s by the Newcastle Soroptomists after falling into disrepair.
Newcastle Recreation Reserve, which includes King Edward Park, was added to the State Heritage List in 2021. The rotunda and surrounding lawn are often used for weddings, events and picnics.
The rotunda lawn was damaged in July 2022 after a vehicle drove onto the grass and left deep tyre marks following a period of wet weather.
The council is encouraging anyone with information that may assist police with their investigation to contact Crime Stoppers.
