More than 54,000 households have been affected by the flooding countrywide, with 6000 of those being in the capital, Nairobi, according to the Interior Ministry.
Dozens of schools and hospitals across the country have flooded, and 17 roads have been cut off.
Mudslides have also forced thousands to move from the western Rift Valley area, while people living downstream of the Tana and Athi rivers have been urged to move to higher ground as water levels in the country's hydroelectric dams rise.
Landslides were reported in Tharaka Nithi, Elgeyo-Marakwe and Kiambu counties in central and eastern Kenya, Kenyan police said in a statement.
"The National Police Service has confirmed the loss of 18 lives as a result of these incidents, underscoring the grave danger posed by the ongoing weather conditions," the police said.
The Kenya Meteorological Department warned that enhanced rainfall is expected to continue in the first two weeks of May.
It is the second time in less than two months that parts of Kenya have endured deadly floods. In March, floodwaters in parts of Nairobi killed at least 37 people.
Experts have warned human-induced climate change is exacerbating weather conditions in Kenya and other east African countries.
with Reuters