The protests were mostly peaceful, although there were clashes around the plaza after police tried to disperse protesters with tear gas and water-launch trucks, as the latter responded by throwing stones.
Voters will be asked to decide between convening a constitutional convention to craft a new national charter and making further reforms to the existing document
Hundreds of people also gathered at the Costanera Center shopping mall - next to South America's tallest skyscraper Gran Torre Santago - with dozens of protesters entering the premises.
During a public event, President Pinera said, "The measure "represents major relief, some help at a time when so many Chilean families need it".
On Friday, thousands of protesters gathered again in Plaza Italia, the centre of the demonstrations in Santiago and the site of weekly rallies that have seen massive turnout since the social upheaval broke out.
No police officers have been killed in the demonstrations but the human rights institute said some 1,600 officers have been wounded.
The Plaza Italia, the ground zero of the protests and renamed by the protesters as "Plaza Dignidad" (Square of Dignity), once again became the epicentre of a large gathering.
Chilen President Sebastian Pinera has announced plans for a dialogue with the citizenry, but the protesters show little interest in talking with the government.
In Santiago, more than thousands gathered in the main Plaza Italia square, with some attempting to make their way to the heavily cordoned presidential palace and engaging in clashes with riot police.
"Chile has changed and the government has to change too," to face the new reality in one of Latin America's most developed countries, he added.
