The capital has been rocked by heavy arms fire between forces loyal to the president and those of the vice president, causing widespread casualties and raising fears the country is returning to civil war.
The United Nations has condemned the fighting in Juba and said it was ready to send more peacekeepers to South Sudan.
Oenone Chadburn, from Christian charity Tearfund, told Premier's News Hour their staff in the country are safe, but need prayers.
She said: "We've spoken to our country director... they're in good spirits.
"We do regularly pray for them as an organisation, and we would ask you to be praying for them, for their safety, their welfare, but once again please pray that we can support those communities who're really badly affected across the whole of the country."
Ms Chadburn went on to say that getting aid into the city is vital.
She said: "This is the capital city, this is the place where all coordination of international aid happens, and it's absolutely vital that we maintain good access for goods to come into the country so we can get them out to the worst affected areas, which are facing a very, very big food crisis."
The UN Security Council held a three-hour emergency meeting on Sunday, and "condemned in the strongest terms" the escalation of fighting in Juba.
It expressed "particular shock and outrage" at the attacks on UN compounds and protection of civilian sites. The council urged an immediate end to the fighting, stressing that "attacks against civilians and UN premises and personnel may constitute war crimes".
One Chinese officer has been killed, and several Chinese and Rwandan peacekeepers were wounded in the attacks.
Security Council members also expressed their readiness to consider enhancing the UN peacekeeping mission in South Sudan in an effort to prevent and respond to the violence.
South Sudan is trying to emerge from a two-year civil war caused by political rivalry between Salva Kiir Mayardit, the president, and Riek Machar, the opposition.
The two rival leaders issued a joint call for calm after Friday's fighting which began outside the presidential compound where they were meeting and soon spread through the city.
A similar skirmish in December 2013 sparked off the civil war that killed tens of thousands of people.
Oenone Chadburn told Premier that churches in the country have an opportunity to help: "Previously when there was massive displacement... it was the church that was offering whole parts of land that they had just to house internally displaced people and these people were coming to these camps and being served and cared for by the church."
Listen to Premier's Antony Bushfield speak to Oenone Chadburn here:
