Violent clashes and heavy shooting took place on Saturday between armed tribal groups in Yambio, capital of South Sudan's Western Equatoria State, according to state information minister.
The clashes left scores of young people and government soldiers dead, said Charles Kisanga, Western Equatoria State Information Minister, in a statement, without giving specific number of the victims.
"The clashes prompted panic among the population in the city", he noted, adding that the clashes forced the majority of the citizens to flee the city to a nearby United Nations mission base.
South Sudan plunged into violence in December 2013, when fighting erupted between troops loyal to President Kiir and defectors led by his former deputy Machar.
The conflict soon turned into an all-out war, with the violence taking on an ethnic dimension that pitted the president's Dinka tribe against Machar's Nuer ethnic group.
The clashes have left thousands of South Sudanese dead and forced around 1.9 million people to flee their homes.