The health ministry said samples tested on Wednesday had confirmed the presence of the Zaire strain of the virus.
It said the initial signal for the outbreak came when a 34-year-old pregnant woman was hospitalised in Kasai province on August 20 with symptoms including high fever and vomiting.
It did not say whether the woman had died.
The World Health Organisation said case numbers were likely to increase as transmission was ongoing.
Ebola is a rare but often fatal illness in humans.
It is transmitted through contact with blood and other bodily fluids.
The WHO said it was delivering supplies including personal protective equipment, mobile laboratory equipment and medical supplies to the inaccessible region, which is a day's drive from Tshikapa, the provincial capital and has few air links.
The province lies to the east of Kinshasa and borders Angola to the south.
"We're acting with determination to rapidly halt the spread of the virus and protect communities," WHO Africia regional director Mohamed Janabi said.
DR Congo has recorded more than a dozen outbreaks, the last one in 2022 in the Equateur province.
A devastating 2018-2020 outbreak killed nearly 2300 people.
The WHO said DR Congo had a stockpile of treatments as well as 2000 doses of the Ervebo vaccine that will be transported to Kasai to vaccinate contacts and frontline health workers.
It will deliver two tonnes of supplies including mobile laboratory equipment and medical supplies.
with DPA
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