The National Disaster Operations Centre could only confirm 20 deaths but said that about 50,000 people had been forced to flee their homes by rising water.
Mudslides have become more common because so many forests have been cleared to make way for farmland, officials say.
The heavy rains are likely to continue for at least the next few weeks, said an official from Kenya's National Meteorological Centre.
The worst flooding is in the low-lying districts of Kisumu and Busia near Lake Victoria, said the centre's spokesman Colonel Bonventure Wendo.
Buried alive
In two separate incidents, mudslides have killed 15 members of two families near Mount Kenya.
Ten relatives were buried alive by a landslide on 30 April as they slept in their home in Meru.
In Muranga, also near Mount Kenya, a similar incident killed five members of the same family, the police said in a statement.
Deforestation means that trees no longer stop earth from sliding down hill-sides, said Mr Wendo.
"In some areas where we never had problems, people have cut trees to cultivate and the soil gets loose," he told the Associated Press news agency.
"We have gone on full alert countrywide, telling those people who live on slopes to move to firmer ground until the end of rain season."
Connections
Last week, President Moi said he would take "drastic action" to stop deforestation.
Most of Kenya's forests are on government land.
But many forests, especially near Mount Kenya and in the Rift Valley, have been sold to people with government connections.
A series of hydro-electric dams built on the south-eastern Tana river has also contributed to the flooding.
Most of the dams are now over-flowing, reports the French news agency, AFP.
Between 30,000 and 50,000 people have been asked to abandon their homes near the river and move to higher ground, said Mr Wendo.
These are the worst floods to hit Kenya since 1998.