At least 78 people were killed in devastating flash floods and landslides that hit the picturesque Brazilian city of Petropolis, turning streets into torrential rivers and sweeping away houses, officials said on Wednesday.

Rescue workers raced to find survivors buried in the mud and wreckage after heavy storms on Tuesday dumped a month's worth of rain in three hours on the scenic tourist town in the hills north of Rio de Janeiro.

There were fears the death toll, which rose steadily through the day, could climb further still as firefighters and volunteers dug through the remains of houses washed away in torrents of mud, many of them in impoverished hillside slums.

It is the latest in a series of deadly storms to hit Brazil in the past three months, which experts say are being made worse by climate change.

The state government said at least 21 people had been rescued alive. Using dogs, excavators and helicopters, rescue workers were urgently searching for more before it was too late.

Around 300 people were being housed in shelters, mostly in schools, officials said. Charities called for donations of mattresses, food, water, clothing and face masks for victims.

Governor Claudio Castro said: "It looks like a scene from a war. It's incredible," he told a news conference.

He praised rescue workers for managing "to save a large number of people before it was too late".

Videos posted on social media from on Tuesday's rains showed streets in Petropolis, the 19th-century summer capital of the Brazilian empire, fill with violent floods that swept away cars, trees and nearly everything else in their paths.

Many shops were completely inundated by the rising water, which gushed down the streets of the historic city center, leaving jumbled piles of overturned cars in its wake.

Officials said more than 180 firefighters and other rescue workers were responding to the emergency, aided by 400 soldiers sent in as reinforcements.

City hall declared a "state of disaster" in the city of 300,000 people, which sits 68 kilometers north of Rio.

The city council declared three days of mourning for victims.

Rescue workers search for survivors after floods and landslides in Sao Paulo earlier this month

Petropolis is a popular destination for tourists fleeing the summer heat of Rio.

The area is known for its leafy streets, stately homes, imperial palace - today a museum - and the natural beauty of the surrounding mountains.

Tuesday's storms dumped 258 millimeters (10 inches) of rain on the city in three hours, nearly equal to all the rainfall from the previous month, the mayor's office said.

The heaviest downpour had passed, but more moderate rain was expected to continue on and off for several days, authorities said.

Sniffer dogs have been brought in to help to find survivors

President Jair Bolsonaro, on an official trip to Russia, said on Twitter he was keeping abreast of "the tragedy."

"Thank you for your words of solidarity with the people of Petropolis," he told President Vladimir Putin after meeting the Russian leader.

"May God comfort (the victims') families."

Brazil has been swept by heavy rains in the past several months that have caused a series of deadly floods and landslides.

Experts say rainy season downpours are being augmented by La Nina, the cyclical cooling of the Pacific Ocean, and by the impact of climate change.

Because a warmer atmosphere holds more water, global warming increases the risk and intensity of flooding from extreme rainfall.

Last month, torrential rain triggered floods and landslides that killed at least 28 people in southeastern Brazil, mostly in Sao Paulo state.

There have also been heavy rains in the northeastern state of Bahia, where 24 people died in December.

It is not the first time the mountains around Rio have been the scene of deadly storms.

In January 2011, more than 900 people died in the region due to heavy rains that caused flooding and landslides in a large area, including Petropolis and neighbouring cities Nova Friburgo and Teresopolis.