World Vision fears more clashes in the eastern provinces of the Democratic Republic of Congo will force thousands of people to flee.
The UN combat brigade established to bring stability to the region opened fire on M23 rebels threatening the border city of Goma on Friday.
The action was taken after M23 shelled buildings in the city centre on Thursday morning.
It is the first time the two forces have clashed and at least five people were killed and dozens more were reported injured.
The fighting has already caused many people to desert the areas of Virunga, Mabanga and Majengo, just outside the city.
Felix Basse, the military spokesman for MONUSCO, the UN peacekeeping force, confirmed: "M23 fired shells south of Muningi, killing a woman and a child of 17 years. Wounded civilians were evacuated to the Heal Africa hospital in Goma."
Frances Charles, the advocacy manager of the charity World Vision's Eastern DRC region, was at a meeting just five minutes away from where the shells rained down.
Charles, who is currently at the World Vision office awaiting security updates, said: "I was immediately aware of the bombardment and concerned that the fighting could escalate.
"We have already seen intense displacement this year with thousands of families fleeing their homes in the countryside to seek refuge in the relative safety of Goma. With hostilities breaking out within the city, we are likely to see many people having to move on again."