The World Health Organisation said on Wednesday that 57 cases and 35 deaths have been reported since the outbreak was announced by Congolese authorities on September 4.
The fatality rate is over 61 per cent.
It is the first Ebola outbreak in 18 years in Kasai province, a remote part of Congo characterised by its poor road networks.
It is located more than 1000km from the nation's capital of Kinshasa.
"We urgently need our partners and donors to step up and support this lifesaving response to ensure we can contain the outbreak quickly and protect the most vulnerable communities," said Susan Nzisa Mbalu, head of communications for the International Federation of Red Cross and Red Crescent Societies Africa.
Earlier this week, the IFRC said it is appealing for $25 million (A$38 million) to help contain the outbreak and aiming to reach 965,000 people with urgent assistance.
It warned that health facilities are overwhelmed and lack the resources to provide care, with clean water and protective equipment running critically low.
According to the IFRC, the only treatment centre in the Bulape health zone, where the epicentre of the outbreak has been declared and the majority of cases are concentrated, is already at 119 per cent capacity.
Health officials are particularly concerned about the impact of US funding cuts, especially since the US has a history of supporting Congo's past Ebola outbreaks.
Despite the absence of USAID, Mathias Mossoko, the Ebola Response Coordinator in Bulape, said that the US government has provided "some small support," though he could not provide specific details.
WHO spokesperson Tarik Jasarevic told the AP on Thursday that the organisation's only current funding for the outbreak response is a $2 million (A$3.06 million) emergency fund and around $2.3 million (A$3.5 million) from the United Kingdom, Germany, and the Gavi vaccine alliance.
That is far below the WHO's projected cost of around $20 million (A$30.6 million) to respond to the outbreak over the next three months.
"Without immediate support, gaps in operations will persist, jeopardising efforts to contain the outbreak and protect vulnerable communities," Jasarevic said.
Treating Ebola demands "enormous resources," even for a single patient, said Jean Paul Mbantshi, the chief medical officer of the Bulape health zone.
He said the zone desperately needs ambulances to transport patients from remote areas to the hospital before they become highly contagious.
Health workers also require more protective equipment, medicine, and additional vaccines.
"All this costs money; we need more support," Mbantshi said.
According to the WHO, just 1740 people in three health zones of Kasai province — Bulape, Bulambae and Mweka — have been vaccinated as of September 21.
The Bulape zone alone has a population of more than 212,000, according to 2020 figures from the United Nations.
