South Sudan fighting leaves 150 troops dead
"The number of casualties is over 150 killed," said Roman Nyarji, a spokesman for rebel leader turned Vice President Riek Machar.
"We are expecting a bigger number of casualties because the two units of the presidential guard were all engaged yesterday," he said referring to bodyguard units of Machar and his rival President Salva Kiir.
Clashes erupted when the two leaders met at the at the presidential palace and initially involved their bodyguards before pouring out to the rest of Juba.
Kiir and Machar described Friday's violence as "unfortunate".
Tense calm followed the dramatic night with heavy security presence overcrowding the civilian-free streets on Saturday morning.
The violence fell on the eve of the country's fifth anniversary of independence - indicating yet more tension to a shaky peace deal that has so yet to calm a civil war that broke out in December 2013.
An August 2015 peace deal was supposed to end the conflict but observers say the peace process has stalled while fighting has continued despite the establishment of a unity government.
Tens of thousands of South Sudanese have died in more than two years of civil war. Close to three million have been forced from their homes and nearly five million survive on emergency food rations.
The humanitarian crisis takes place alongside an economic one with the currency collapsing and inflation spiralling out of control. The country's mainstay oil industry is in tatters and regional towns have been razed.