Pope Francis has called for an end to the plundering of the Amazon basin as he closed an assembly of Catholic bishops who discussed the challenges facing the church in the region.

The work of the Vatican assembly, known as a synod, ended last night with a final document containing a proposal that married men in the remote area be allowed to be ordained as priests.

The milestone proposal could lead to a landmark change in the church's centuries-old discipline of celibacy.

One of the other themes of the three-week synod was the environmental protection of the vast Amazon Basin and respect for its approximately three million people and the cultures of their four hundred or so tribes.

In his sermon at this morning's Mass in St Peter's Basilica, Pope Francis criticised those who consider indigenous people "backward and of little worth" instead of acknowledging what their cultures can teach others.

"They despise their traditions, erase their history, occupy their lands, and usurp their goods. How much alleged superiority, transformed into oppression and exploitation, exists even today!" he said.

He admitted that, "even in the church", there were those who scoff at the poor or silence them as inconvenient.

The Argentinean pope made an apparent reference to the excesses of European Christian colonisers who began arriving in the region almost 500 years ago.

"The mistakes of the past were not enough to stop the plundering of other persons and the inflicting of wounds on our brothers and sisters and on our sister Earth: we have seen it in the scarred face of the Amazon region," he said.

The synod's final document warned of the risks to the Amazon basin from mining and deforestation, which scientists say increases the threat of global warming.

The bishops proposed that the church define what would constitute the "ecological sin" of harming the environment and also introduce specific ministries for the care of nature.

The pope will consider the proposals, including an expanded role for women, in writing his own post-synodal document, known as an Apostolic Exhortation. He said he hopes to have it ready by the end of the year.

At the mass, attended by indigenous people from the Amazon, the pontiff also appeared to take a swipe at conservatives who have attacked parts of the synod's working document as heretical.

His opponents, inspired by the writings of two cardinals, held several side events during the three-week-long assembly.

They took particular umbrage at the use of an indigenous statue of a pregnant woman at an opening event, saying that was pagan.

The pope asked forgiveness for what he considered an insult to the indigenous after ultra-conservative Catholic militants stole replicas of the statue and dumped them into the Tiber River.

In his sermon, Francis spoke of "those masters of the art of self-justification" and those seeking "self-canonisation".

The gathering of 184 Catholic bishops drafted the final document after considering presentations from representatives of indigenous peoples and other laypeople, including nuns and experts.

They discussed a multitude of regional concerns, from the destruction of the rainforest and the global climate emergency, to land-grabbing and the exploitation of indigenous peoples.

The synod used a definition the vast region, which includes all or parts of Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Peru, Venezuela and Suriname.

Most are countries where most of the population is Catholic but where evangelical Protestant churches are becoming increasingly popular.

Additional reporting Joe Little