Fires they thought were contained 24 hours after they started Saturday kicked up again with Sunday afternoon's winds and raged out of control, threatening more neighborhoods.
With no municipal water or fire hydrants to use, routes to the blazes blocked by narrow streets jammed with abandoned vehicles and countless embers being stoked, fire crews could do little but watch some neighborhoods burn.
From the sky, 20 helicopters and planes were mobilized to drop water on hotspots, but Chile's national emergency office said the battle was far from won.
"This won't be extinguished, not today nor tomorrow," the office tweeted after issuing a new alert when fires kicked up again Sunday afternoon.
The blaze began in a forested ravine next to ramshackle housing on one of Valparaiso's 42 hilltops, and spread quickly. Hot ash rained down over wooden houses and narrow streets. Electricity failed as the fire grew, turning the night sky orange and reducing neighborhoods on six hilltops to ashes.
Schools were closed Monday in the city, since some were damaged and others were overflowing with evacuees.
President Michelle Bachelet toured the shelters and canceled this week's trip to Argentina and Uruguay, ordering her ministers to meet with her Monday morning to explain their responses. "It's a tremendous tragedy. This could be the worst fire in the city's history," she said.
Valparaiso is a picturesque oceanside city of 250,000 people surrounded by hills that form a natural amphitheater. The compact downtown includes Chile's congress and its second-largest port. But most of the people live in the hills, and the city owes its status as a UNESCO World Heritage Site to their colorful homes, built on slopes so steep that many people commute using staircases and cable cars.
But what's beautiful in postcards can be dangerous for those who live there: Many people have built on land not fit for housing, and entire communities lack municipal water connections.
"We are too vulnerable as a city. We have been the builders and architects of our own danger," Valparaiso Mayor Jorge Castro said Sunday in an interview with Chile's 24H channel.
The fires destroyed at least 2,000 houses by Sunday evening, and the death toll rose to 12, Interior Minister Rodrigo Penailillo said. Three of the 12 victims were identified, and the others are so badly burned that DNA tests will be done, the national forensics service said. More than 500 people were treated at hospitals, mostly for smoke inhalation.
It was already the city's worst fire since 1953, when 50 people were killed. Bachelet declared the entire city a catastrophe zone and put the military in charge of maintaining order. Some 1,250 firefighters, police and forest rangers battled the blaze while 2,000 sailors in combat gear patrolled streets to maintain order and prevent looting.
Chile's emergency response system generated automatic phone calls to each house in danger as the mandatory evacuations expanded. Many people stuffed their cars with possessions after getting these calls, and streets quickly became impassible. Water trucks and firefighters were stuck downhill as people abandoned their vehicles and ran. Some carried television sets and others took canisters of natural gas, fearing an explosion if flames reached their homes.
Shelters were overflowing.
"I had to flee when I saw the fire was coming down the hill," said Maria Elizabeth Diaz, eight months pregnant and trying to rest with her two sons at Valparaiso's Greek School. "I lost everything. Now I've been ordered to rest because I was having contractions. My little one knows that he can't arrive quite yet."