A clever orang-utan called Karta has made a bid for freedom by short circuiting an electric fence in Adelaide Zoo.

Visitors to the South Australian Zoo watched in amazement as the 137lb primate piled up debris close to the wall, then jammed a stick into the wiring while using branches to pull herself up over the concrete and glass wall.

The Zoo was immediately evacuated as Karta sat on top of a ledge for around 30 minutes before voluntarily returning to her enclosure.

Zoo keeper Paul Whitehead explained that the 27 year old animal was highly intelligent and had a history of trying to outsmart her keepers.

In a counter-intelligence plan, keepers intend to clear her enclosure of any vegetation that could be used in a future bid for freedom.