The incident on Sunday occurred at Hell's Gate National Park in the Rift Valley region, Kenya Wildlife Service (KWS) said on its Twitter account.
"Search and rescue operation for three missing tourists under way in Hell's Gate National Park. Two more bodies were recovered overnight, bringing the total number of the dead from the tragic flash floods to four people," KWS tweeted on Monday.
The group included five Kenyan tourists, a local guide and a non-resident whose nationality was not disclosed. KWS said the gorge in the park was closed to the public on Sunday after the incident.
Two survivors from the group alerted park rangers, who sent out a search party, AFP news agency reported.
The park is famous for its steam plumes from geothermal activity under its ground, and in areas adjacent to it, the steam is harnessed to generate electricity. Established in 1984, the park is home to three geothermal stations.
Gorges in the park are prone to flash floods and have in the past killed visitors. In 2012, floods killed seven who were part of a church group on a trek.
Hell's Gate is around 100km northwest of the Kenyan capital, Nairobi, and just south of Lake Naivasha.