Santiago de Chile, April 17 (Xinhua-RHC) -- The devastating forest fire in the Chilean port of Valparaiso was extinguished Wednesday after claiming at least 15 lives and leaving some 12,500 residents homeless in five days, the city's Fire Department said.

The fire "is completely extinguished," Valparaiso's fire chief Enzo Gagliardo said. "The weather helped us, we've had a lot of drizzle and quite a lot of nighttime humidity."

In their struggle to contain the blaze, city firefighters, composed entirely of unpaid volunteers, received help from their counterparts from other cities, including the capital Santiago.

The National Forest Corporation (Conaf) remains on alert against possible new fire eruptions in surrounding hills.

Authorities have ruled out arson as a possible cause.

Prosecutor Jaime Andrade, tasked to determine the cause of the blaze, said "the line of investigation, which is being confirmed through work at the site of the incident and eyewitness testimony, indicates the fire was not set intentionally."

One preliminary theory is that strong winds could have caused electrical lines running across a forested area to short circuit, sparking a fire that spread quickly from home to home in areas unregulated by urban development.

The blaze, considered the worst in the city's history, ignited on Saturday and spread across several densely-populated hilltops, destroying more than 2,000 homes, mostly low-income ones, and razing about a thousand hectares of land.The fire came barely two weeks after a powerful 8.1-magnitude earthquake shook Chile's northern Tarapaca region, killing six people and destroying at least 3,000 homes.

Chilean President Michelle Bachelet has said her administration is studying a plan to improve Valparaiso's urban infrastructure, and promised to rebuild the city in a way that is "better and more worthy" of its status as a World Heritage City.