The Narok-Maai Mahiu road has been temporarily closed after a section of a bridge collapsed at Siyabei area, next to Maasai Mara Technical Institute, following heavy rainfall.
Kenya National Highway Authority Assistant Director, Corporate Communications, Charles Njogu said advised motorists to use alternative routes.
"Accordingly, KeNHA has temporarily closed the road for urgent restoration works as from tonight," he said in a statement.
The route connects Nairobi to Narok, Maasai Mara Game Reserve, Bomet, Kisii, Luo Nyanza and Tanzania.
Motorists heading to Nairobi from Homa Bay, Kuria, Migori Kisii, Bomet and Narok told to use the Kericho-Nakuru route.
The meteorological department has warned heavy rains will continue in many parts of the country, causing flooding.