"Two hundred and fourty two women have been taken into medical care," said Cris Baguma, a local Congolese doctor with the International Medical Corps (IMC) at Walikale.
Most of the rapes were in Luvungi, a settlement of some 2,160 people, and in surrounding villages, the IMC said.
The IMC blames the attacks on Hutu rebels of the Democratic Forces for the Liberation of Rwanda (FDLR) and local militias.
"The most striking cases were those of two pregnant women and another who had given birth two weeks earlier," said Baguma, adding that the eldest of the victims was 75 and the youngest 16.
"Women told us they were stripped and left naked, some had their breasts pulled, almost all were beaten, and some were bitten," said Christophe Nyembo, an IMC psychologist.
Nyembo added that the territory around Walikale "is a crossroads for mining sites. The aggressors thought the women were hiding gold in their genitals and pushed in their fingers."
Both doctors said that in the cases of some women raped in front of their husbands, the men told their wives to seek medical attention, which is rare in eastern DR Congo, where men tend to cast off raped spouses.
IMC staff stressed that there could be other victims who have not yet been treated and others in health centres that the charity has still to visit.
The United Nations on 23 August reported that at least 179 women in Nord-Kivu were raped between 30 July and 3 August by the FDLR, which has denied it, and by local Mai-Mai militia.
On Tuesday, UN Special representative on Sexual Violence in Conflict, Margot Wallstroem, threatened to have people suspected of these rapes prosecuted for war crimes.
The FDLR has been active in eastern DR Congo since the mid-1990s and is feared for its brutality. Its older members are accused by Rwanda of taking part in the 1994 genocide of 800,000 people, mainly minority Tutsis, in the neighbouring country.