Protesting natives supported by opponents of President Rafael Correa brought Ecuador's capital to a standstill, demanding an end to policies they say will open the Amazon rainforest to vast mining projects and ravage the environment.
Thursday's protests were prompted partly by a recent agreement between Ecuador and China for industrial copper mining in the Amazon's Ecuacorriente Zamora-Chinchipe region.
Supporters of the leftist president, however, also came out in force, raising fears of violence between the rival groups were high.
"We did not come to destabilise," said Humberto Cholango, head of the Confederation of Indigenous Nationalities of Ecuador (CONAIE), a powerful umbrella group that represents natives from around the country.
The group supported Correa when he was elected in 2007, but later split and accused him of abandoning them in favour of free-market policies.
Protests led by CONAIE, which claims to represent a third of Ecuador's population of more than 14 million, have already toppled two presidents, Abdala Bucaram in 1997 and Jamil Mahuad in 2000.
However Correa, who polls show has an 80 per cent approval, also has support among Ecuador's natives.
Some 1,000 natives carrying a giant rainbow flag entered the capital from the south after a two-week march from the Amazon rainforest town of El Pangui, some 700 kilometres to the south.
Another group of around 500 natives entered Quito from the north, and were joined by leftist activists and members of a teacher's union. The groups were set to meet in the downtown El Arbolito park.
Correa spoke earlier to thousands of his supporters who gathered at the same park, then marched to a plaza next to the government palace.
"We will never talk to the corrupt right, with the liars!" Correa told them. He later urged the natives to not let themselves "be used."
"We know that mining is necessary for modern life. As well as the raw materials, we need the revenue so that we can care for handicapped people, pay for social security, build roads," the president told local radio on Thursday.
Correa said the country's first ever large-scale mining deal, which was signed with Chinese-owned Ecuacorriente earlier
this month, guarantees the government, not the miners, will receive most of the income from mineral exports.
"These are the best negotiated contracts ever in world history," he said. "We got as much out of them as was possible."
The government called supporters to gather for defence against a possible coup.