A violent storm that spawned a tornado and mudslides killed at least 15 people across northern Argentina and southern Brazil, authorities said Tuesday. Dozens were injured in the winds and hail as their homes were destroyed.

At least 10 died in Argentina, said Ricardo Veselka, civil defense director for the town of San Pedro, where the twister hit.

Four people were killed in the Brazilian city of Guaraciaba, and one person died in a Sao Paulo slum after a mudslide swept into ramshackle homes, civil defense officials said in a statement on their Web site. Civil defense earlier reported two victims there, but later lowered the death toll without explanation.

Rescue workers in Sao Paulo searched the rubble Tuesday evening for three people still missing and were also trying to find two children believed buried after part of a school collapsed, according to civil defense officials.

The worst damage was in the small Argentine towns of Santa Rosa and El Progreso, where officials said houses and even a city health center were blown away early Tuesday. Trees fell on cars, blown down by winds of more than 60 mph.

"Whole houses disappeared," Veselka said. "There are posts down, trees down, and there are more than 50 injured."

Extremely heavy rains tangled traffic in Sao Paulo for most of the day and cut off phone service in some neighborhoods. Two rivers overflowed onto major highways in South America's largest city.