The resignation of Pope Benedict XVI has surprised the Archbishop of Sydney, George Pell, who says the world's leading Catholic always worked to do what was best for the church.

The 85-year-old pontiff announced on Monday he would retire on February 28, citing health and age reasons.

Cardinal Pell, who will travel to Rome to take part in the election of a new pope, said the church would pray for Pope Benedict as he enters retirement.

"His resignation came as a surprise to me," he said in a statement on Tuesday.

"We thank him for his years of devoted leadership and service and his brilliant teaching."

The resignation of the Pope, who was chosen to lead the Catholic Church in April 2005, is an unusual move that has shocked many around the world.

The last pope to resign was Pope Gregory XII, who stepped down in 1415.