Restoration work on Athens' Acropolis is set to shift to the west side of the Parthenon under a 40-year-long effort to restore the ancient archaeological monument, officials said Thursday.

"Most of the restoration work was completed in 2015, whereby we fixed the most important and urgent problems," the head of the operation Vassiliki Eleftheriou told AFP.

"Now we need to address certain other areas such as the west pediment," she said.

For visitors to the hill-top citadel, the project means a crane, which has been parked in front of the Parthenon, will now be moved inside the ancient temple to repair the northern wall, she added.

Most of the work involves bolstering the pillars of the pediment and removing rusty iron supports dating from the early 20th century that had caused further damage to the monument.

No cost estimate was given.

The restoration phase will last a year but other tasks are expected to continue to 2020, Eleftheriou said.

The Parthenon's western pediment once depicted a legendary contest between Poseidon, god of the sea, and Athena, goddess of wisdom, for the patronage of Athens.

Like most of the temple, the pediment was damaged during a Venetian siege in 1687.

In addition, the best sculpture remnants were subsequently removed in the early 19th century on the orders of British ambassador Lord Elgin, who sold them to the British government.

Despite the economic crisis plaguing Greece since 2010, the Acropolis restoration works have never ceased thanks to European support funds.