The violence, which has killed a total of 13 people since Thursday, stems from disputes between the government and members of the Buganda, one of Uganda's four ancient kingdoms. Members of the Buganda ethnic group have clashed previously with the government over land rights.
Barricades of burning tires were erected in Kampala as stone-throwing mobs roamed the streets, underlining growing tensions in a nation hailed for its relative stability and economic growth.
Some unemployed people also reportedly joined the rioting.
The possibility that the violence will continue on Saturday increased after police said they would prevent Buganda King Ronald Muwenda Mutebi II from traveling to a political rally. The government's refusal to allow the trip on security grounds sparked the first day of rioting Thursday, with the king's supporters insisting he should be allowed to move freely.
On Friday, an Associated Press photographer saw a 13-year-old boy shot in the head and another man shot in the back as stone-throwing protesters fought running battles in the streets with police. The boy's mother, who did not give her name, said a soldier in an armored personnel carrier shot her son as he stood outside a store. A woman also was killed, police said.
About 15 miles (25 kilometers) from the capital, three people were killed in riots, police said. One man died from stray bullets and two were beaten by rioters, said the area security officer, Dan Bidigo.
Shops were closed and roads were fairly empty in the capital Friday. On the outskirts of town, protesters built burning roadblocks and set a bus alight. Police patrolled in armed vehicles.
Uganda's traditional kingdoms were banned in 1966 but reinstated by President Yoweri Museveni in 1993. But Museveni has restricted their leaders to a largely ceremonial role to avoid potential political rivals.
Members of the kingdom make up Uganda's largest ethnic group and there is friction between the Buganda and members of the smaller Banyara tribe, who claim the Buganda refuse to recognize them.
Five radio stations were suspended for inciting violence.
Analyst Solom Male said the riots are becoming a focal point for other groups dissatisfied with the government.
"Those people rioting on the streets are unemployed and poor," he said. "The government has not addressed their problems."