Firefighters backed by police and soldiers spent a third day Monday battling a massive blaze that has killed 15 people and ravaged a huge swath of Chile's historic port of Valparaiso.

It could be yet another two days before they succeed in extinguishing the fire, whose cause is under investigation, officials warned.

So far, the inferno has consumed 1,140 hectares (2,817 acres) and 2,500 homes, leaving 11,000 homeless, according to Interior Minister Rodrigo Penailillo.

Some who refused to leave their homes died when the flames swept through.

Hardest hit have been Valparaiso's poorer neighborhoods, perched precariously on the coastal city's tinder-dry hillsides, where dwellings built mostly of wood with tin roofs quickly became engulfed.

Thick smoke has settled over the city and ash from the fire rained down on its historic port, which so far has been spared the wrath of the blaze.

President Michelle Bachelet has declared the ravaged area a disaster zone, allowing the armed forces to assist in relief efforts and take control of security.

"We are in an ongoing emergency situation," Defense Minister Jorge Burgos told local radio, adding that the fire poses "a very complex situation."

At least 11 helicopters, six planes and 2,000 police and soldiers, in addition to battalions of firefighters, are battling the blaze.

They were heartened by a forecast of cooler temperatures and higher humidity, which was expected to slow the fire's advance.

The city, an architectural gem located about 80 miles (120 kilometers) from the capital Santiago, is famed for its UNESCO-listed center with cobblestone streets and brightly painted wooden homes.

The fire broke out in woodland on Saturday and, whipped up by winds, quickly became fast moving, forcing 10,000 people to evacuate.

- 'I will not leave' -

Some residents -- including a few who later died -- had refused the order to evacuate for fear of losing their possessions to flames or looters, even though police and emergency crews guarded the streets.

"I will not let go of what little I have. This represents 15 years of effort, and until I can no longer see my house, I will not leave it. My wife and my four children are in a shelter," said Arturo Gomez.

About 1,200 people had spent a second night in one of eight such shelters set up by authorities.

Some people who dared venture back after fire tore through their neighborhoods discovered homes that had been reduced to smoldering ruins.

Health Minister Helia Molina said that, in addition to reconstruction, counseling would be offered to those affected.

"We are working with counseling teams to take charge of helping with what it means for a family to lose everything it had because in this case people lost everything."

The blaze sparked the second mass evacuation in Valparaiso in as many weeks after the city was at the center of a tsunami alert following a magnitude 8.2 earthquake on April 1.

The fire also poses a new challenge for Bachelet, who one month after taking office on a mission to narrow the gap between rich and poor, must re-order her priorities.

Bachelet announced she was postponing a visit to Argentina scheduled for Tuesday, in what was to have been her first trip abroad after taking office for a second term on March 11.

Valparaiso's golden era was from the mid-19th century to the early 20th as a stopover point for ships steaming down South America and to round its southern tip into the Atlantic Ocean.

Fires occur frequently in central Chile, where summer sends temperatures soaring. It is currently fall in the Southern Hemisphere.

In February 2013, some 105 homes were destroyed in Valparaiso, affecting 1,200 people.