Among the dead in clashes at Kilelengwani village are eight children and nine police officers. Many of the dead suffered spear and machete injuries, the Red Cross said.
The aid group said 167 houses were set on fire when the village was attacked by more than 300 people, in a situation described as still volatile.
Reuters news agency said some 100 people have been killed in the last three weeks in violence between the Pokomo and Orma ethnic communities, in Kenya's Coast province.
On Friday, 12 people died when armed raiders set fire to houses overnight in what was described as a revenge attack.
The Pokomo and Orma communities have a long history of fighting over land and water resources, in what is one of the poorest regions of Kenya. The Pokomo are a largely settled agricultural people, planting crops along the river, while the Orma are largely cattle-herding pastoralists.
Many of the dead from previous attacks were women and children who were hacked to death with machetes or burned alive.
In addition to the ethnic clashes, Kenya has been the target of grenade attacks after its troops crushed Al Shabaab Islamist militants in Somalia last year.
The country's second-largest city, Mombasa, was hit by violent protests following the death of a Muslim cleric accused of helping Al Shabaab.
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