The Conservation Regulator has launched an investigation into the incident which occurred near some cliffs just north of Portland early this week.

Upon arriving, authorities found the trees had holes drilled into their base where herbicide was then poured in.

While the situation remained an active investigation, a conservation regulator spokesperson warned the acts were a criminal offence.

"Poisoning native vegetation on Crown land is a criminal offence as it damages the environment and destroys wildlife habitat," they said.

Anyone with information is encouraged to report it to 136 186. All information will be treated as confidential.

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The attack comes just days after two of the century-old trees in Warrnambool's Nicholson Street were found with drill holes and fresh wood shavings.

It's the third time the city's trees have been targeted, following an incident directly opposite on another tree on the street's north side in mid-2020 and again in January this year, when new holes were found near the base of the trees.

Warrnambool City Council's trees and botanicals team leader John Sheely said he hoped the trees would reshoot, but the odds were unlikely.

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