Heavy rains killed at least 10 people and left a trail of destruction in Rio de Janeiro on Tuesday, raising questions about the city's preparedness to deal with recurring extreme weather.

Torrents of water gushed down streets, sweeping up cars and uprooting trees after rains that began around rush hour Monday evening. Rains slowly weakened by Tuesday evening, but Mayor Marcelo Crivella said the city was still in "crisis" mode, the highest of three levels.

Schools were closed and people were urged to avoid non-essential traffic until further notice.

City officials said 152 millimetres of rain fell in just four hours Monday night, more than the average for the whole month of April.

A street in Rio damaged by heavy rains. Officials closed schools and urged people to avoid non-essential traffic. (Silvia Izquierdo/Associated Press)

The botanical garden neighbourhood, a tourist destination, was one of the most badly hit areas, receiving 231 millimetres in a 24-hour period. Local television stations showed firefighters in that neighbourhood wading through knee-deep water pulling a small boatload of children evacuated from a school bus on a flooded street.

Sirens sounded in 20 flood-prone areas of the city, alerting people to make their way to pre-established safe spaces.

But no alarm was given in the Babilonia slum, which sits on a hill behind the iconic Sugarloaf mountain. The fire department said two women there died in a mudslide, and local residents complained about the lack of warning.

The mayor, acknowledging the city's lack of preparedness for the deluge, said sirens did not sound in Babilonia because the water had not reached the minimum threshold to activate the alarms. He said officials would look into lowering this threshold in the future.

What it looks like when that much rain falls in so little time:

Parts of Rio de Janeiro were no match for the hundreds of millimetres of rain that poured down over just four hours Tuesday. 0:34

Hillside slums are particularly vulnerable to mudslides and city officials said more than 100 communities in Rio have been identified as having "high geological risks." Crivella said Rio has plans to improve safety, but complained of a lack of federal funding.

The mayor said a recent study carried out by the city identified about 200,000 road potholes and rainwater networks that needed fixing, pressing President Jair Bolsonaro for more federal funding.

"We're talking about hundreds of millions" of reals, the mayor said on Globo TV news (one Brazilian real is about 35 cents Cdn).

An abandoned vehicle sits in floodwaters. The mayor is calling for hundreds of millions of Brazilian reals to fund better flood preparedness. (Silvia Izquierdo/Associated Press)

A storm with torrential downpours and strong winds just two months ago killed six people, prompting Rio residents to ask what the city is doing to protect them from routine weather events.

Rio's fire department said that by Tuesday evening it had registered 10 deaths from the latest storm, including two adults and a child who were buried in a car by a mudslide. According to news portal G1, the three victims were a little girl, her grandmother and their taxi driver.

Firefighters spent hours trying to reach the vehicle, going through mud, rubble and fallen trees.