Pope Francis has hit out at the global financial system and the deregulation of financial markets for the "cult of money" and blamed it for causing growing inequality across the world.

In his first major speech on the six-year-old financial crisis, Francis told ambassadors at the Vatican that world leaders needed to reform the global financial system to make it more ethical and concerned for the common good.

"Money has to serve, not to rule," Francis said.

The 76-year-old Argentinian pope blamed a culture of greed for the widening gap between a rich minority and a poor majority.

"While the income of a minority is increasing exponentially, that of the majority is crumbling," he said.

"This imbalance is due to ideologies promoting markets' absolute freedom and financial speculation, which prevent governments from exercising their right to control [on financial institutions] for the common good," Francis said.

"Nowadays human beings are considered as expendable consumer goods."

In his speech, the former Buenos Aires cardinal Jorge Bergoglio slammed corruption, tax evasion and the invisible tyranny of market laws.

"We cannot be part-time Christians. We should seek to live our faith at every moment of every day," he later tweeted from his account, @Pontifex.

Bergoglio, who succeeded Pope Emeritus Benedict XVI in March, took the name of Francis from St Francis of Assisi, saying that the founder of the Franciscan Order's devotion to the poor should work as an example for the whole Catholic Church from the top down.

"The Pope loves everyone, rich and poor alike, but the Pope has the duty, in Christ's name, to remind the rich to help the poor, to respect them, to promote them," Francis concluded.