Nkayi, also known as N'kayi, is a town and a commune in the Bouenza Department of the Republic of the Congo. It is the country's fourth lar…Nkayi, also known as N'kayi, is a town and a commune in the Bouenza Department of the Republic of the Congo. It is the country's fourth largest city with a population of 104,083. Nkayi is a major sugar production centre in the country.