Around 5,000 firefighters, police, forest rangers, soldiers, sailors and civil defence workers have joined the fight against devastating wildfires circling the Chilean city of Valparaiso, with the death toll rising to 15 people.

Helicopters and planes dropped water on the flames and smouldering ruins of some of the city's poor neighbourhoods throughout Monday, the third day since flames first erupted in a forest on the outskirts of the city and were then spread by strong winds that scattered embers into slums.

The entire city was under military rule by Tuesday.

Navy officer Julio Leiva said another body had been discovered in the wreckage on Monday, raising the toll to 15. More than 500 people had been treated at hospitals, mostly for smoke inhalation.

An estimated 11,000 people were homeless as the toll of destroyed homes rose to more than 2,500. A contingent of sailors in riot gear stood ready to evacuate another 700 families whose homes could be lost if the winds shifted.

The fires have been so hot they created their own fierce winds, spreading flames that consumed a few entire neighbourhoods of ramshackle houses. Homes stood unscathed in other districts but remained in danger from the embers being whipped through the air.

'Weeks' to stamp out

"We are looking at the largest air operation ever assembled against a fire like this," Michelle Bachelet, the Chilean president, said. She said the blazes had grown to "dimensions never before seen".

Chile's forestry agency predicted it would take three weeks to completely stamp out the fires.

Some people left shelters set up by authorities on Monday and made their way home only to discover ruins. Hundreds of young volunteers climbed up the hills to carry bottles of water and shovels to help the victims pick through the wreckage.

"We're going to rebuild right here. Where else would we go?" said Carolina Ovando, 22, who lost the humble home where she had lived with three small children.

Schools have been closed, some of them damaged by fires and others jammed with evacuees.

Bachelet, who decreed the city under military rule, coordinated the emergency response with her cabinet, cancelling a trip to Argentina and Uruguay. She asked Chile's neighbours for backup in case of other fires, freeing Chilean planes and helicopters to join the fleet in Valparaiso.

Valparaiso is an oceanside city of 250,000 people surrounded by hills that form a natural amphitheatre. The compact downtown includes Chile's congress and its second-largest port, and the city owes its status as a UNESCO World Heritage Site to the colourful homes built on slopes so steep that many people commute using stairs and cable cars.

But what's beautiful on postcards can be dangerous for those who live there: Many people have built flimsy homes on land not fit for housing. Many of the poor neighbourhoods have no municipal water or sewerage connections, fire

hydrants or streets wide enough for emergency vehicles.

"We are too vulnerable as a city. We have been the builders and architects of our own danger," Jorge Castro, the mayor of Valparaiso, said in an interview with Chile's 24H channel.