Everyday they cross the border from Nigeria on motorbikes, donkeys or even on foot, and all are looking for safe haven from the Islamist militants of Boko Haram.

They arrive at the already teeming refugee camp in Minawao in northern Cameroon, where they join the thousands of Nigerians who have fled the insurgency in their home country that's killed some 10,000 people.

"Sometimes 70 of us sleep here, sometimes 80," refugee Apollos Luka said, pointing at the tent that he has lived in with family for the past three months.

The population of the camp, which squats on an arid plain ringed by mountains, has shot up to 18,000 from 6,000 in just two months.

The United Nations High Commissioner for Refugees estimates that 4,000-5,000 more arrive each week in the far north of Cameroon, which butts up against Boko Haram's fiefdom of Borno state.

About 70 percent of those new arrivals are women and children who need immediate assistance in the form of food, shelter and medical care.

The UN's special representative for central Africa Abdoulaye Bathily warned Thursday the refugee situation there is on the verge of a disaster.

"If nothing is done urgently, it is very likely that a humanitarian catastrophe will follow that would further complicate the security challenges," he said.

Since Boko Haram launched its campaign in 2009 to take control of Nigeria some 40,000 Nigerians have sought refuge in Cameroon and another 100,000 have done so in Niger.

'TOO DANGEROUS'

People living in the camp told AFP of risky sanitary conditions, meagre food rations and overwhelmed services.

"When they (refugees) arrive there are no toilets... people cook and do their business outside, it's terrible," said Luka. Camp officials admit they had to rush to build toilet as well as water facilities and were unprepared for such an influx of humanity.

An elderly refugee Barma Mala said, as his hands shook, that it's nearly impossible to get enough to eat.

"There is not enough food, they distribute rations once per month only," he said. "We eat nothing but rice and corn."

Meanwhile at the camp's primary school 16 teachers are responsible for educating some 1,500 students who turn up for hugely overpopulated classes in electric blue uniforms.

"We do what we can to teach them to write, read and count. But it's complicated in these conditions," said teacher Albert Tamta, who has 156 students in his class. "We lack a lot of things, especially notebooks."

Some have already endured these conditions for years, with no end in sight. Boko Haram recently denied it had agreed to a ceasefire, as was claimed by the government.

"It's impossible to go home, it's too dangerous," said refugee Ayuba Ishaku, who fled Gwoza in northeast Nigeria a year ago. "I would like to work here in Cameroon, but they do not speak the same language as we do. I feel a bit lost."

Adding the pain of being displaced, is the fear that the refugees have not been able to fully escape the violence in Nigeria, with kidnappings and attacks multiplying in Cameroon these past months.

Some refugees have spotted -- and turned in -- suspected Boko Haram militants in their midst and an elite unit of the Cameroonian army periodically seals off the camp and carries out searches.

The soldiers have already made several arrests, an unnamed humanitarian aid worker told AFP, but added, "it's impossible to check everything".