The Kenya Red Cross tweeted on Thursday that 39 people had been taken to hospitals, and that efforts to find and rescue more victims were still underway.
The flooding struck at about 9 p.m. Wednesday in and around Solai, a cluster of villages northwest of Nairobi. Local reports identified the failed structure as a privately owned earthen dam on a large farm.
Samuel Gachobe, who represents the area in Parliament, said the government was trying to identify the missing, and was providing food, blankets, bedding and medical care to people who had fled. A command center was set up to coordinate aid and rescue efforts, he said in a statement.
Last week, the Red Cross reported that more than a month of torrential rain had killed about 100 people and displaced about 260,000 in Kenya; that about 100,000 people were reported displaced in Somalia, and that there was flooding in Ethiopia and Rwanda, as well. The region faced a drought last year.
The flooding is the worst in Kenya since 2012, said Marshal Mukuvare, the regional disaster management delegate for the International Federation of Red Cross and Red Crescent Societies.