The European Union said it estimated more than 200,000 people in CAR were displaced internally by conflict and another 55,000 have fled the country.
European Commissioner for Crisis Response Kristalina Georgieva said humanitarian agencies are working under "exceptionally challenging" circumstances in a country the International Committee of the Red Cross says is long forgotten.
"The entire population of more than 4 million people is affected by the ongoing crisis and suffer as a result of looting and violations of human rights," the commissioner said in a statement. "The situation is rapidly deteriorating. We must act now."
The rebel Seleka coalition is accused of committing war crimes in its campaign in CAR. The movement toppled the government in March.
Georgieva is touring the country with U.N. Emergency Relief Coordinator Valerie Amos.
"The needs in CAR are huge and are increasing," Amos said.
Georgieva said Thursday she was releasing $10.2 million in emergency assistance for CAR.