One resident told Reuters that they had found at least three bodies in the morning but more people were missing as residents dig through thick mud following the incident.
There were reports of a further 25 killed in a village some 50 kilometers from Bukavu, a city of an estimated two million people in South Kivu province, and the death toll was expected to rise.
Emmanuel Majivuno Kalimba, a Bukavu city official, said the damage was made worse because of waste dumped by residents which clogs up the city's waterways.
The provincial government in a statement said it would conduct an investigation to determine the reasons for the material damages.
"It rained a lot in Bukavu, the water took more than 25 people last night, we ask the provincial and national government to help us," said neighborhood leader Patrick Baka Wa Bana.
Town hall spokesman Joseph Mugisho Zihalirwa told AFP that at least 19 people had been killed and five injured in one district alone — including 11 members of the same family swept away by a river that burst its banks.
Albert Migabo Nyagaza, a local official and a pastor, said that a wall collapsed on worshippers during a church service, killing five people.
He added that three other people were swept away in flooding.
Mao Ishikitilo, a territorial administrator south of Bukavu, said that about 20 people had died in his area, without giving further details.
AFP said it was unable to independently confirm the death toll from the landslides.
The DRC is one of the world's poorest nations, despite its immense mineral wealth. It is regularly hit by disasters such as floods and landslides, in part due to urban overcrowding, dilapidated infrastructure and shoddy house construction.
On Tuesday, torrential rains triggered landslides in the city of Kananga in the center of the country, killing at least 22 people.
Information in this report came from Reuters and Agence France Presse.
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