Tens of thousands of people who fled Boko Haram in northeast Nigeria are facing a severe lack of water, compounding widespread food shortages and security fears, aid workers said Monday.

For the past week supplies have been low at the Muna camp for internally displaced people (IDPs) in the city of Maiduguri after one of its five solar-powered water pumps broke down.

"We are facing a serious water shortage in the camp," said camp coordinator Tijjani Lumani, adding that the four other pumps on the sprawling site were "inadequate".

Muna camp, on the edge of the city, is currently home to some 41,000 people, Lumani said.

The water drawn up from boreholes is used for cooking and, crucially, washing to prevent the spread of disease through the densely populated compound of makeshift tents.

"The water shortage poses a serious health risk to IDPs because they may have to turn to other unclean water sources, which exposes them to water-borne infections like cholera and diarrhoea," said one aid worker involved in sanitation and health projects for IDPs living in Maiduguri.

"The situation is more alarming when malnourished children are involved," said the worker, who asked not to be identified.

Borno state governor Kashim Shettima confirmed on Sunday that there was a "breakdown of water supply" at the camp but engineers were trying to fix the problem.

"The State Emergency Management Agency has so far supplied 105,000 litres of water using trucks," he said in a statement on his Facebook page.

Boko Haram's Islamist insurgency has killed at least 20,000 people and forced more than 2.6 million others from their homes since it began in northeast Nigeria in 2009.

But as the military opens up areas formerly in rebel hands, the true scale of the devastation has emerged, revealing people cut off from food supplies and unable to plant crops.

The United Nations has said 7.1 million people are "severely food insecure" in northeast Nigeria and parts of neighbouring Cameroon, Chad and Niger that have also been hit by the conflict.

Conditions in parts of Borno state are "famine-like", it has said.

Boko Haram has continued to target IDPs and there have been several attempted suicide bomb attacks near Muna camp, which is not fenced off and is easily accessible.

Insecurity compounded by theft has also stymied efforts to rebuild.

In Bama, a city 70 kilometres (45 miles) from Maiduguri which was once home to 270,000 people, 40 people were arrested earlier this month for allegedly stealing construction materials.

The head of Nigeria's security and civil protection body, Ibrahim Abdullahi, told AFP that in the space of a week his agents recovered a huge array of materials the suspects had taken from building sites, including "cement, zinc roofing sheets, iron rods, copper wire, electric power generators, rugs, car batteries, television sets, fans, sewing machines and air conditioners."

AFP