This photo shows the flooded streets in Petropolis, Brazil, on Tuesday. Reuters

At least 18 people died in mudslides and floods when torrential rain swept a mountainous region of Rio de Janeiro state, and there were fears the toll could rise as searchers check damaged areas on Wednesday.

Brazilian firefighters said that landslides and flooding triggered by heavy rainfall is the cause behind the killing in tourist town.

The state fire department said late on Tuesday that more than 180 soldiers were already working in the stricken Petropolis region, which saw hundreds of deaths from heavy rainfall in 2011.

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"So far, 18 deaths caused by landslides and floods have been confirmed" in recent hours, the Rio de Janeiro Fire Department said in a statement.

It said more than 180 firefighters and other rescue workers were at the scene in the picturesque hill town of Petropolis where Brazil's last emperor Pedro II is buried, 68 kilometres (42 miles) north of the city of Rio.

People stand among flooded streets in Petropolis, Brazil, on Tuesday. Reuters

The department said the area got 25.8 centimetres (just over 10 inches) of rain within three hours Tuesday — almost as much as during the previous 30 days combined.

City hall declared a "state of disaster" as images spread on social media of destroyed houses and cars swept away by floodwater.

Many shops were completely inundated by the rising waters which gushed down the streets of the historic city center.

Some parts of Petropolis received up to 260 millimeters (10 inches) of water in less than six hours, more than was expected for the whole month of February, according to the meteorological agency MetSul.

More than 180 soldiers were already working in the stricken Petropolis region.

Footage posted on social media showed cars and houses being dragged away by landslides and water swirling through the city of Petropolis and neighboring districts.

The heaviest downpour had passed but more moderate rainfall was expected to continue for several hours, authorities said.

President Jair Bolsonaro, on an official trip to Russia, said on Twitter that he was keeping abreast of "the tragedy" and asked his ministers to provide "immediate aid to the victims."

Earlier this month, floods and landslides caused by torrential rain killed at least 28 people in the southeast of the country, mostly in Sao Paulo state and the region north of Rio.

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

Petropolis’ city hall said in a statement that the heavy rains left "a high number of incidents and victims” and that rescue and recovery efforts were continuing.

Brazilian President Jair Bolsonaro, who is on a trip to Russia, said on Twitter that he instructed his ministers to deliver immediate support to the afflicted.

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