BUENOS AIRES, Argentina (AP) -- A natural gas explosion destroyed a tall apartment building in the Argentine city of Rosario on Tuesday, killing at least five people, injuring more than 50 and causing an evacuation of much of the downtown.

Dozens of people were trapped in the upper floors of the burning building as a huge plume of smoke went up over the country's third-largest city. The building's front and back facades were ripped open, exposing the shattered remains of apartments inside.

Firefighters worked from above and below to pull people to safety as the bottom floors burned. The blast damaged other buildings for blocks around, and fearing a collapse, police closed buildings and schools in a five-block radius.

The Litoral Gas company also cut off the gas flow to much of the downtown.

Municipal Health Secretary Leonardo Caruana told Argentina's Todo Noticias channel that a young man and woman were among the five dead, but released no other information about the victims.

"The 51 injured are in public and private hospitals across the city," he said, adding that three of them had critical injuries.

Rosario's Civil Defense director, Raul Rainones, told the local Diarios y Noticias agency that the explosion appeared to have been caused by a gas leak.

The fire took three hours to extinguish, and left the building in serious danger of collapse, firefighters said.

Buildings were damaged for several blocks surrounding the blast, which sent bricks and glass and cement crashing down to the street. A total of 11 schools were evacuated, and several shops and other apartment buildings were damaged.

Security Secretary Sergio Berni offered the services of the border police and coast guard to help local authorities.