Pope Francis on Saturday appointed a senior Vatican diplomat as his new Secretary of State, ousting divisive cardinal Tarcisio Bertone as he looks to overhaul the Church's scandal-ridden administration.

His replacement for the "number two" position at the Vatican, Italian cleric Pietro Parolin, is currently the Catholic Church's envoy to Venezuela and has worked on improving ties with communist China.

"The Holy Father has accepted... the resignation of His Eminence Cardinal Tarcisio Bertone," the Vatican said in a widely-expected announcement, adding that the changeover would formally take place on October 15.

At 58, Parolin is seen as relatively young for top Vatican office and observers say he could help a process of renewal within the Church, as well as making it more influential on the world stage.

The Argentine pope has shown a strong reformist drive in his first few months in office and has set up a series of committees aimed at reforming the Vatican hierarchy, its economic affairs and its bank.

"I feel the full weight of the responsibility placed upon me: this call entrusts to me a difficult and challenging mission, before which my powers are weak and my abilities poor," Parolin said in a statement.

He was previously a Vatican envoy to Mexico and Nigeria and has worked on sensitive issues for the Church, including diplomatic relations with Israel.

Religious affairs expert Gianni Valente, writing for the Vatican Insider website, said Parolin was cast "in the true spirit of Vatican diplomacy".

Valente said Parolin would ensure that the Church "will once again be well placed to offer its wisdom and foresight in order to promote peace" in the world.

Italian President Giorgio Napolitano said Parolin's appointment would help "enrich" relations between Italy and the Vatican and promote joint work between the two "to protect peace and justice".

Bertone has held the post since 2006 when he was named by the pope's predecessor Benedict XVI and has proved a highly controversial figure in the hierarchy.

Leaks by Benedict XVI's butler last year revealed infighting between pro- and anti-Bertone factions inside the Vatican corridors of power.

Critics say he has made poor choices in a series of key Vatican appointments and has shown favouritism.

He was at Benedict's side during an extremely difficult period for the Vatican, shaken by revelations of widespread child abuse by priests and several scandals involving its finances.

Francis has circumvented the Secretariat of State, effectively the central administration of the Roman Catholic Church, on key decisions in recent months.

However, it is also traditional for new popes to replace some top officials appointed by their predecessor and Bertone was already over the usual age of retirement of 75 for senior Church figures.

Parolin was ordained in 1980 and his first foreign posting for the Vatican was in Nigeria in 1986, followed by Mexico in 1989 where he fought to gain legal recognition for the Catholic Church.

In 1992, he was called back to Rome to work for the Secretariat of State and was appointed to a position equivalent to a deputy foreign minister in 2002.

In 2009, he was appointed papal nuncio to Caracas.

The Vatican also on Saturday said it was confirming some top Secretariat of State officials named by Benedict, as well as the previous pope's close aide Georg Gaenswein who will remain as head of the pontifical household.

Gaenswein is still secretary to Benedict, who lives in retirement in a former monastery inside the Vatican walls, and will therefore continue in an unprecedented dual role serving both the pope emeritus and the pope.