Weeks of heavy rains that began in mid-August have left much of Mauritania's capital city, Nouakchott, and six of the surrounding regions under water, creating "unprecedented" damage according to the Department of Civil Protection.
Some areas have seen as much as 35 percent more rainfall than average, according to the National Meteorological Office.
More than 5,600 people have been affected by the flooding, according to the International Federation of Red Cross and Red Crescent Societies (IFRC). The Office for the Coordination of Humanitarian Affairs (OCHA) says that 2,305 people have been displaced and at least eight people have died.
The worst-affected communities are in the department of Moudjeria, in Tagant, south-central Mauritania, where the Mauritanian Red Crescent Society (MRCS) reports that 40 percent of families have lost their homes.
In addition to the estimated 525 homes that were washed away or collapsed, schools, market places, health centres and other public buildings have been destroyed by water damage. Many roads have become impassable and entire neighbourhoods in some regions remain inaccessible.
In parts of the southern agricultural zone, fields have been flooded, which the World Food Programme (WFP) warns could affect harvests.
In the north, herders in flooded areas lost whole herds - and thus their entire livelihoods. Young children's nutrition could severely deteriorate, as under-fives are primarily fed goat's milk. IFRC warns these groups need urgent food aid.
Some 800,000 Mauritanians, or 20 percent of the population, is estimated by WFP to be food insecure.
Following the first wave of heavy rains, the government's Food Security Commission (CSA) - the body that manages flooding disasters - mobilized to drain flood water and deliver food and tents to those worst affected. At the end of August, the government announced that it would allocate US$3.5 million for continued relief efforts.
Aid agencies, however, were much slower to respond - partly, they say, because the government failed to ask for outside help.
"One must understand that in Mauritania, everything is organized and driven by the state," said Aliou Boly, IFRC operations manager in Mauritania. "So it is the state that is involved in the response, and the humanitarian actors who contribute help on the basis of the demands made by the CSA."
The International Committee of the Red Cross (ICRC) says is not working on the flooding for the time being. "The authorities have not yet declared it as an emergency, or called upon international organizations," said ICRC head in Mauritania Rania Machlab.
Several humanitarian agencies met on 29 August to put in place an assessment team. On 19 September, OCHA met with the governor of Nouakchott to propose outside help, and held an inter-sectorial meeting to coordinate relief efforts.
The first official request for help was sent to the international community on 28 September by the mayor of Sebkha, a suburb of Nouakchott.
Rapid needs assessments have shown that emergency shelters in rural and semi-rural areas are among the most pressing requirements. Non-food items, including soap, kitchen sets, mosquito nets, sleeping mats, blankets, water purification tablets, jerry cans and other household and hygiene items are a priority for those families who belongings were washed away. OCHA says access to drinking water and health services is also crucial.
Some organizations, such as the IFRC and Médecines Sans Frontières (MSF), have begun relief efforts, but many agencies say they are still assessing the situation and developing a plan of action.
MRCS has distributed tents, utensils and kitchen sets in Tagant and Brakna in the southwest, and will continue assistance for three months, including training people on proper hygiene under difficult water and sanitation conditions.
WFP says it has been working with partners to assess the impact of flooding on the upcoming harvest and will plan food assistance accordingly.
In Nouakchott - which lies below sea level and lacks a functional drainage system - World Vision and the Department of Civil Protection have begun draining water.
The prime minister has also deployed a special task force to drain water in the region's worst-hit areas, according to OCHA.
But floodwater has shown little sign of receding, say aid agencies. "The water just isn't moving, and it's become quite dirty," said IFRC's Boly. "It's true that water is being pumped out in many areas, but the pace isn't fast enough to keep up with the falling rain. Not only does this standing water pose access problems, but it is major health threat."
MSF has a team on the ground supporting a health centre in the capital, and it has been clearing out waste and stagnant water to reduce the risk of water-borne disease. It plans to work with the Ministry of Health to gather data on the prevalence malaria and cholera.
Many health centres are still unable to resume operations. With the start of the school year approaching, authorities say it is unlikely that the damaged schools will be ready to open in time.
Economic activities, particularly in Nouakchott, are also suffering, as many businesses remain closed and customers lack money, said traders.
OCHA reports that many people have become frustrated by what they feel is a lack of response on behalf of the government. There have been reports of violent protests throughout affected areas, including Nouakchott's Sebkha suburb, where youths took to the streets on 16 September and sieged a local senator's house.