High-Rise Office Building in Downtown Madrid, Spain Engulfed by Flames, Top Floors Collapse

MADRID, Spain -- Firefighters struggled Sunday to control Madrid's worst blaze in recent memory, unable to extinguish the flames raging through one of the city's tallest office buildings.

The fire, which left seven people slightly injured, broke out in the 32-story Windsor building Saturday at about 11:20 p.m. (2220GMT). Thick smoke and searing temperatures were still preventing firefighters from entering the building on Sunday night.

''This is the biggest fire ... this city has ever had,'' Mayor Alberto Ruiz-Gallardon told reporters outside the blackened hulk of twisted wreckage in Madrid's business and banking district.

Gallardon said the building was in danger of collapsing, and ordered nearby businesses to remain closed for the next few days. The operation of three subway lines running under or near the damaged building would also be curtailed, he said.

It was not immediately clear what caused the fire, but the building was almost empty when the first alarm went off. Only one of the seven firefighters who suffered smoke inhalation remained hospitalized Sunday, Gallardon said.

Although the flames were no longer visible from outside by Sunday night, gray smoke and ash stoked by gusts of wind continued to pour from the blackened shell of the building.

Earlier in the day, several top floors collapsed onto lower ones. Firefighter official Fernando Munilla said the entire building _ which at about 106 meters (350 feet) high is among the 10 tallest in Madrid _ could collapse.

''If the partial collapses keep happening, it would be lying to say it's impossible that the whole building couldn't fall down,'' he said.

Emergency crews at the scene said firefighters were waiting for the temperature inside the building to drop, which they said would lessen the danger of collapse.

At their peak, temperatures reached 800 degrees Celsius (1,472 Fahrenheit), said Javier Sanz, head of Madrid's firefighters.

''Technically we can't say that the fire is under control,'' Gallardon said. ''The situation is still critical.''

Prime Minister Jose Luis Rodriguez Zapatero visited the site to thank the emergency crews battling the blaze.

''I wanted to thank all those people who have been working since early in the morning, firefighters, police, and all those who have thrown themselves in to help in this catastrophe,'' Zapatero told reporters.

Thousands of onlookers lined streets barred to traffic.

''It gives you a sense of insecurity'' to think that fire could destroy a modern building so fast, said Paola Mendez, an office worker from another part of town. ''It's not that old. Was it well built?''

Construction of the shiny gold Windsor Building began in 1973 and was completed in 1979. It became a landmark structure in Madrid's business district. The building was surrounded with scaffolding due to recent repairs, and a huge crane remained perched on its roof.

Associated Press writer Mar Roman contributed to this report.