Five tourists and a guide were on Sunday been reported missing after being swept away by flash floods in Hell's Gate National Park in Naivasha.
Rift Valley Regional Police Commander Marcus Ochola said the police and Kenya Wildlife Service personnel have been dispatched to the area to search for the six.
"Our major problem is that it is already dark and it is going to be difficult to conduct the operations, but we are trying our best," Mr Ocholla said.
The Hell's Gate, which lies south of Lake Naivasha, and which was once a tributary of a prehistoric lake that fed early humans in the Rift Valley, experiences floods because of the gorges that lie downhill.
Even when it has not rained, water from other regions of Nyandarua and Nakuru Counties flow to the gullies in Hell's Gate in huge volumes.
Police officers from Nakuru and Nyandarua counties led by Nakuru County Police Commander Stephen Matu are at the site to help in rescue operations.
Hell's Gate, which was established in 1984, has in the past claimed the lives of several domestic and international tourists.
In 2012, eight members of a Nairobi church youth group were swept away by flash floods.
The site which is gazetted as a National Park under the Ministry of Tourism is managed by the Kenya Wildlife Services, KWS and covers an area of about 68 square km.