About 1,500 troops from Bangladesh, Pakistan, Indonesia and Morocco, among other nations, will join 4,800 African troops already on the ground who will be "re-hatted" to serve in the MINUSCA mission.
Senior UN officials and CAR's President Catherine Samba-Panza are to attend a formal ceremony in Bangui on Monday to launch the UN's 9th mission in Africa and 16th worldwide.
The mission was set up in April, taking over from the African Union-led MISCA that was deployed alongside 2,000 French troops after a March 2013 coup plunged the country into bloodshed and chaos.
A ceasefire deal signed in July has yet to take hold, and the appointment of the country's first Muslim prime minister has done little to put CAR back on track to reconciliation.
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The violence has wiped out what little state authority was being wielded from Bangui in one of Africa's poorest countries. It ranks 185 out of 187 on the UN development index.
"The state has always been extremely weak but it has got to the point where ministers have an office and a building of sorts, maybe they have a personal assistant, maybe a computer, and that's it," said UN peacekeeping chief Herve Ladsous.
Under a deal signed with the Bangui government, UN peacekeepers will be tasked with restoring law and order and given authority to make arrests. They also will ensure that prisons are guarded and courts are operating.
"We have to give citizens a feeling that the state is back," said Ladsous.
To help rebuild central power, UN officials are also looking at ways to bring millions of dollars from diamond mines now in the hands of militias back to state coffers.
The mission is facing a mammoth logistical challenge in a country with appalling roads and a smattering of airstrips. Equipment trucked in from Douala, in nearby Cameroon, takes at least 10 days to reach Bangui.