Vandals have destroyed a 155-year-old monument and graffitied another in Melbourne’s Flagstaff Gardens overnight.

The Pioneer Monument appeared to be in pieces on Thursday morning, with the words “death to ‘Australia'” graffitied at its base.

An obelisk monument in a Melboune park.

The inscription on the Pioneer Monument says it was “erected in 1871 to the memory of some of the earliest of the pioneers of this colony whose remains were interred near this spot”. (Supplied: City of Melbourne)

The Pioneer Monument was created by Samuel Craven and erected in 1871, according to the City of Melbourne’s website.

Its inscription reads: “Erected in 1871 to the memory of some of the earliest of the pioneers of this colony whose remains were interred near this spot”.

The Separation Memorial was also graffitied with the words “land back” but remained standing.

According to the council, the Separation Memorial dates to 1950 and marks the 100th anniversary of the proclamation of the Victorian Government.

Both monuments are in Flagstaff Gardens in West Melbourne, on the edge of the city’s CBD.

The graffiti also included red triangles painted on the monuments.

Police confirmed they were investigating and said they believed the vandalism occurred between 10pm on Wednesday and 6am on Thursday.

They said it was believed machinery was used to pull down the Pioneer Monument.

Monuments to be repaired, Lord Mayor says

Melbourne Lord Mayor Nick Reece said the council was also involved in the investigation.

“Defacing or damaging city assets in Melbourne will not — and cannot — be tolerated,” he said in a statement.

“While there are a range of views on statues and memorials, each time a monument is damaged it’s ultimately the ratepayer footing the bill — and that is unacceptable.

“We can have a debate about the future of statues and memorials, but we will never tolerate or reward vandalism.”

A rectangular brick monument is spray-painted with the words 'Land Back' in red paint.

The Separation Memorial marks the 100th anniversary of the proclamation of the Victorian government. (Supplied)

Speaking further to ABC Radio Melbourne, Cr Reece said the monuments would be repaired, noting the Separation Memorial marked an important event in Australia’s democratic history.

“The Separation Memorial actually memorialises Separation Day, the day that Victoria became a colony in its own right,” he said.

“It was actually a great step forward for democracy for the people of the state.”

He described the vandals as “idiots”.

“These are low-IQ individuals who don’t actually understand the historic significance of the monuments that they are attacking,” he said.

The vandalisation and destruction of statues and monuments tied to colonialism have become common in the lead-up to Australia Day on January 26.

Last year, sites targeted included a memorial to John Batman, known as the modern-day founder of Melbourne, and an Anzac memorial.Â