Heavy rain brought Brazil's biggest city of Sao Paulo grinding to a halt on Tuesday and reportedly claimed the lives of six people in landslides.

The bodies of four brothers aged five to 20 were recovered by firemen from a house that crumbled apart in one landslide in a northwestern suburb, CBN radio, Globo Television and the Terra news website all said.

Reports also said two more people died in other parts of the city, while authorities evacuated 22 homes in an eastern suburb because of fear the ground there could shift too.

The persistent rain brought traffic on key cross-city highways to a standstill as the adjacent Tiete and Pinheiros rivers broke their banks.

Television images showed trucks and motorbikes driving through long stretches of water-covered roads, while vehicles piled up for kilometers (miles) on other impassable routes.

Access to the city's international airport of Guarulhos was difficult, with the main road to the facility cut off.

The Climatempo weather service said it was the heaviest 24-hour period of rainfall Sao Paulo had seen all year. Overnight alone, the city received half of its total average December precipitation.

The state Emergency Administration Center declared an alert, saying the rain would continue with "light to moderate intensity," creating the "potential for new flooding."

Sao Paulo mayor Gilberto Kassab assured reporters that his services were prepared to handle the consequences of the bad weather, and he denied repeated accusations that lack of investment in water canalization was to blame.

Farther south, 161 towns in the state of Rio Grande do Sul bordering Uruguay declared a state of emergency because of the rain. The region had already been lashed by storms over the past few weeks that killed eight people and forced 14,000 from their homes.