Chileans will vote on Sunday on whether they want the country's Pinochet-era constitution torn up and replaced by a fresh charter drafted by citizens, a key demand in protests that erupted last year.
The fiery anti-government protests over inequality and elitism in one of Latin America's most advanced economies broke out last fall and resumed with the easing of coronavirus lockdowns.
Voters have 12 hours beginning at 8 a.m. (1100 GMT) to cast their ballot.
Citizens can decide whether to approve or reject a new constitution and whether it should be drafted by a specially elected citizens' body, made up half of women and half of men, and indigenous representatives, or a mix of citizens and lawmakers.
Opinion polls suggest a new charter will be approved by a significant margin.
All eligible Chileans from the country's population of 18 million are automatically registered to vote, but voting is optional.
People with COVID-19 have been told to stay away from voting stations on threat of arrest and prosecution.
Control points have been set up at least 20 meters (22 yards) from polling place entrances where officials will conduct identity spot checks to ensure people are not on the quarantine list.
"The right to vote of an infected subject puts at risk the right to health of thousands of people," Attorney General Jorge Abbott told regional staff in an email.
Soldiers, ubiquitous on Chilean streets since the declaration of a state of emergency during the protests last year and again with the outbreak of COVID-19 in March, will oversee the process inside polling stations while police will guard outside.
The current constitution was drafted by dictator Augusto Pinochet's close adviser Jaime Guzman in 1980, and has only been tweaked by successive governments to reduce military and executive power.