Dozens of people have been killed in clashes in South Sudan's capital Juba, military, medical and journalistic sources have said.
Gunfire broke out on Friday evening near the building where President Salva Kiir was meeting his sometime rival, former Vice-President Riek Machar.
Estimates of the death toll vary, but most accounts put the number over 100 - some as high as 150.
A 2015 peace deal to end a 20-month civil war has failed to quell unrest.
Juba is in lockdown as the world's newest country was set to mark the fifth anniversary of its independence from neighbouring Sudan.
Friday's fighting was apparently sparked by a shootout between Mr Kiir's and Mr Machar's bodyguards. The two men met at the presidential palace on Friday.
The half-hour gun battle then escalated, with heavy weapons and artillery being used in several parts of the city.
In a speech marking independence, Mr Kiir said: "Making South Sudan glorious will only happen if we see ourselves as South Sudanese first rather than tribal or political groupings," Juba's Miraya FM station reported.
He added that everyone in South Sudan should "use our rich cultural diversity as the source of our unity".
South Sudan was rated the second least peaceful country in the world in the Global Peace Index last month.
On Saturday, a South Sudanese journalist said other journalists stuck inside the state house had counted at least 100 bodies, inside and outside the compound.
A hospital doctor told the Associated Press that scores of bodies had been brought in, while a military spokesman for the opposition - Mr Machar's faction - said 115 people had been killed.
Mr Kiir and Mr Machar described Friday's violence as "unfortunate".
Under a peace deal agreed last August, the two armed factions took up positions in Juba in April.
Tens of thousands died in the civil war and millions were forced from their homes.
South Sudan is so short of money that the authorities say no official anniversary celebrations will be held.
The streets of Juba were reported to be quiet on Saturday.
Roadblocks were set up in the capital, with troops searching people for weapons.