Authorities had earlier prevented a representative of Ronald Muwenda Mutebi, the traditional ruler of the Buganda kingdom, from travelling to the region to prepare for a political rally, citing fears of violence.
"They are rioting because (the official) was stopped by police from entering into Kayunga," Judith Nabakoba, a police spokeswoman, told the Reuters news agency.
Buganda is one of the east African nation's four ancient kingdoms that was abolished by former leader Milton Obote in 1966 and restored by Yoweri Museveni, the current president, in the early 1990s.
The kingdoms have historically had tensions with the central government.
The traditional king holds a largely ceremonial position in Uganda, but holds considerable influence among the Baganda.