A full 3.7 million people were displaced within DR Congo by the end of March -- more than double the 1.6 million at the start of 2016, the United Nations humanitarian agency OCHA said.
"This is a massive, massive deterioration," Rein Paulsen, who heads OCHA's country office in DR Congo, told reporters in Geneva.
The situation is particularly dire in the central Kasai region, where spiralling violence between government troops and tribal militias has forced 1.27 million people from their homes since last September, he said.
The fighting in Kasai erupted after government troops last August killed tribal chief Jean Pierre Mpandi, also known as Kamwina Nsapu, who had launched an uprising against President Joseph Kabila.
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Violence in the region has left at least 400 people dead since September.
The UN has meanwhile reported finding 40 mass graves, while two UN researchers -- Michael Sharp, an American, and Zaida Catalan, a dual Swedish-Chilean national -- investigating the violence were abducted and shot dead. One of the victims was also beheaded.
Under a power-sharing deal reached on New Year's Eve, DR Congo is set to hold an election by the end of 2017.
But last week the government said it had indefinitely postponed voter registration in two Kasai provinces after the brutal killing last month of an electoral official.
Most worrying perhaps is that the violence has increasingly taken on an ethnic character, with fighting breaking out between a wide range of communities, Paulsen said.
"Inter-ethnic, inter-communal conflict (is) at the heart of why things are deteriorating so rapidly," he said.
There are currently an estimated 1.9 million children under the age of five in the country suffering from severe, acute malnutrition, meaning they could easily die without immediate aid, Paulsen said.
In light of the dire situation, the UN has appealed for USD 812.5 million for aid to DR Congo in 2017, but so far less than 20 per cent of that amount has been funded, he said.