Vandals, wielding a machete or an axe, have "cruelly destroyed" a decades-old section of Melbourne’s Royal Botanic Gardens.

Staff were devastated when they arrived at work on Wednesday to find almost all of the plants in the Arid Garden had been ravaged. Some of specimens of cacti and succulents that were destroyed are rarely found in the wild, the gardens’ chief executive Tim Entwisle.

The Royal Botanic Gardens' Arid Garden was vandalised overnight, with around 80 per cent of the columnar cacti and succulents destroyed.

It is believed the attack on the attraction, which contained plants up to 30 years old, happened sometime on Tuesday night.

Dr Entwisle said the destruction broke a respect and trust developed over centuries between the general community and public gardens.