The number of people in northern Cameroon who have fled their homes fearing the violence in neighbouring Nigeria and cross-border raids by Islamist sect Boko Haram doubled in March to 117,000, a United Nations survey showed.

Boko Haram, which wants to carve out an Islamic caliphate in northern Nigeria, recently expanded its activities into Niger and Cameroon for the first time since launching its insurgency in 2009.

It has killed 6,400 people in 337 incidents since January 2014, the United Nations has said.

There are some 117,000 displaced people in northern Cameroon, U.N. Sahel coordinator Robert Piper said, almost double the 60,000 recorded a month ago, adding to the strain on scarce resources in an area still recovering from a decade of periodic drought.

"The northern part of Cameroon was already under severe strain due to deteriorating climate conditions over the last three years. The growing insecurity has further exacerbated that situation," Piper told the Thomson Reuters Foundation.

There has been a 300 percent increase in food insecurity in Cameroon since 2012, and three-quarters of those affected are in the north.

Some 228,000 Cameroonian children are believed to be malnourished and 80 percent of them are in the north, according to the United Nations.

Cameroon's Agriculture and Rural Development Ministry has warned there may be famine in the Far-North Region in the coming months as many of those displaced have abandoned farms and moved further from the border for their safety.

Yaounde estimates some 66,000 refugees have fled to Cameroon from northern Nigeria since the start of the Boko Haram insurgency in the three Nigerian states of Borno, Yobe and Adamawa, putting further pressure on the region.

Cameroon has been prioritised as an emerging crisis in 2015 because of the combination of conflict and climate-related problems in the region, according to the minutes of a meeting of U.N. agencies and charities in December, seen by the Thomson Reuters Foundation.

Cameroon has a further 250,000 refugees in the east of the country as a result of insecurity in neighbouring Central African Republic, according to the U.N. refugee agency (UNHCR).

In 2014, Cameroon received just 61 percent of the $126 million sought in emergency funding. This year the United Nations has asked for $264 million in funding, around half of it for the north of the country.

President Paul Biya unveiled a multi-billion dollar emergency plan for the north last year, but money to equip a regional military force that includes Cameroonian soldiers to fight Boko Haram may eat into that pledge, Piper said.