At least 55 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 Wednesday.

Rescue workers raced to find survivors buried in the mud and wreckage after heavy storms 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 could rise further as firefighters and volunteer rescue workers dug through the remains of houses washed away in torrents of mud, many of them in impoverished hillside slums.

At least 21 people have been so far been rescued alive in the effort, according to the state government.

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

Following the incident, Petropolis' city hall declared three days of mourning.

In a Twitter post, Brazilian President Jair Bolsonaro, who is on a trip to Russia, said he had instructed his ministers to deliver immediate support to communities affected.

"May God comfort the family members of the victims," he wrote. 

(With input from agencies)