An hour-long downpour has caused heavy flooding and huge traffic jams in Brazil's biggest city.

Rescue workers from Sao Paulo's fire department say a man was electrocuted when an overhead power line was dislodged by a tree and fell during the thunderstorm.

The torrential rain tuned streets and avenues into rivers and videos posted on news websites showed cars being swept away or submerged.

Authorities declared a state of alert in the worst hit parts of the city.

The heavy rains and flooding came amid the worst drought to hit the city in more than 80 years, but they won't necessarily help replenish the city's nearly dry reservoirs.