The clashes in Tana River district, Coast Province, took place late on Tuesday between the Orma and Pokomo groups, the region’s police chief said.
Most of the dead were women and children, he said. Police have been deployed to the area.
The clash is the worst since post-election violence rocked the country after disputed polls four years ago.
Regional deputy police chief Joseph Kitur said that those killed were either hacked to death with machetes or burned alive.
The victims included 31 women, 11 children and six men, he said, describing it as “a very bad incident”.