A violent storm that triggered a tornado has killed at least 17 people in the southern part of South America and destroyed hundreds of houses.

Northern Argentina and southern Brazil, and the small countries of Uruguay and Paraguay wedged between them, were hit by fierce rain, hail and winds travelling at more than 70mph.

In northeastern Argentina, 10 people died, including seven children, authorities said.

More than 50 others were injured, and trees and power lines were toppled in the towns of Santa Rosa, Tobuna and Pozo Azul, said Ricardo Veselka Corrales, head of the local civil defence office.

Witnesses and local media described the storm as a tornado.

The other seven fatalities occurred in Brazil's southern states of Santa Catarina and Sao Paulo, where flooding and mudslides swept through unstable slums.

Santa Catarina's state civil defence service, which counted four of the deaths, also called the sudden storm "a probable tornado."

South American meteorologists were wary of using the term, although the US National Climatic Data Center said the area affected was the only zone in South America with a likelihood of experiencing such high-speed spinning tubes of destructive wind.

"It could have been a tornado," said Jorge Leguizamon, of Argentina's National Meteorological Service.

"The phenomenon still hasn't been classified. Experts will have to evaluate the damage," he said.

The provincial minister for Argentina's hard-hit area, Daniel Franco, said it was clear that the storm was "not normal for this area."