The Angolan government has been accused of being in denial over a drought that has affected 1.8 million people because the crisis threatens to tarnish the country's image as a booming economy.

Children as young as nine are digging wells to fetch water, amid a severe drought in southern regions of Angola that has forced people to use unclean water for consumption and cooking, according to the UN. Neighbouring Namibia, which has also been badly affected, has declared a drought emergency and appealed for humanitarian aid.

Angola has done neither, although it has appointed a special inter-ministerial commission to respond to the drought, delivered food aid and drilled boreholes. Government sources have told the UN that funding requirements are between $150m (£242.3m) and $350m, but amounts disbursed so far have not been confirmed.

International relief agencies, including Unicef, the World Health Organisation and the Food and Agriculture Organisation, began responding to Angola's drought in 2012, but the Angolan government was slow to respond, according to aid officials.

"At the time, there was a denial of the problem," said an aid official. "There was a lot of difficulty for them to accept the situation. There was a lot of criticism of the methodology of our rapid assessment. The government said it did not need humanitarian assistance and had enough resources … the problem is we don't know how much it has provided."

Others have been harsher, accusing the Angolan government of seeking to play down the crisis.

"We have a government that has no political responsibility," said Elias Isaac, country director for the Open Society Initiative of Southern Africa (Osisa) and a strong critic of the Angolan government. "Last month, it spent over $130m to host an international hockey tournament and paid for the Spanish to come, so you see the lack of regard this government has for its own people."

Unicef, the UN agency for children, says approximately 3 million children under five will potentially be affected by the effects of the prolonged drought. Between December last year and June this year, 17,746 malnourished children went through outreach community programmes, 5,337 with severe acute malnutrition and 11,097 with moderate acute malnutrition.

"The drought follows three years of poor rainfall," said Enrique Paz, Unicef's head of child survival and development in Angola. "In terms of water, access in affected provinces has been limited to ponds that are drying up, with the water unsafe for drinking and cooking. There have been 1,500 cases of cholera, with 62 deaths."

Drinking water is a concern, particularly in Cunene and Namibe. Cunene has been the hardest-hit province, where an estimated 542,979 people – half of Cunene's population – have been affected, especially farmers, including semi-nomadic communities, and children under five. Almost 1.2m livestock are at risk.

Provincial authorities have indicated that 430 water points are not working, affecting 100,000 people. The wells are as deep as 15-25 metres, and dug where a stream has dried up. Children, mostly boys between the ages of nine and 18 have to cover distances of 15-30km to dig wells and fetch water.

Malnutrition has reached 24.4% of the population in Cunene, with a prevalence of severe acute malnutrition of 5.7%. Food production has been badly hit. In some areas – Cunene, Namibe, Benguela coast and the southern part of Huila – almost all production of cereals and legumes was lost.

Poor rainfall has particularly affected five southern Angolan provinces: Cunene, Namibe, Kuando Kubango, Benguela and Huila. Rainfall during the 2011-12 season was 60% below average. Rainfall in 2012-13 was also well below average in large parts of the country, particularly in the southwest on the Namibian border.

The drought comes against a backdrop of strong economic growth. According to the World Bank, Angola's gross domestic product (GDP) is estimated to have grown by more than 8% in 2012, spurred by high oil export price and rising production volume. According to the UN Committee for Development Policy, Angola's gross national product was more than double a threshold of $1,190 per capita a year to qualify for the move from least-developed country status.

Yet sub-Saharan Africa's third biggest economy, which has been ruled by president José Eduardo dos Santos for 34 years, has not seen its oil wealth spread evenly. Spectacular growth has created few jobs and entrenched or even deepened inequality, underlining that natural resources can be both a blessing and a curse.

For Isaac, the Angolan government has been too proud to admit the need for help. "It is a lack of regard for its own people and a question of national pride," he said. "To accept help from other organisations would contradict the picture that Angola is one of Africa's most successful economies ... one thing that needs to happen is for more information, there needs to be more pressures from civil society, churches, particularly the Roman Catholic church, if it doesn't take a strong stand that's a big problem."