U.N. Secretary-General Ban Ki-moon arrived on Sunday in Pakistan to discuss to discuss relief efforts in a tour in the areas hit by devastating flood disaster in which 20 million people were affeted as popular anger mounts over the government's failure to tackle the crisis.

Nearly 12 percent of te population, some 20 million people, have been affected by one of the worst catastrophes in Pakistan's history. Six million still need food, shelter and water, according to the United Nations.

Survivors fought over food being handed out from a relief vehicle close to the town of Sindh, ripping at each other's clothes, and causing such chaos that the distribution had to be abandoned.

The floods, triggered by torrential monsoon downpours just over two weeks ago, engulfed Pakistan's Indus river basin, killing up to 1,600 people, Reuters said.

Lack of food

Only a quarter of the $459 million aid needed for initial relief has arrived, according to the United Nations.

"I am here ... to share my sympathy and solidarity of the United Nations together with the people and government of Pakistan at this time of trial," Ban said on arriving in Pakistan.

"I am here also to urge the world community to speed up their assistance to Pakistan."

Ban met both Prime Minister Yusuf Raza Gilani and President Asif Ali Zardari, who has been a lightening rod for popular anger after travelling to Europe as the catastrophe unfolded and not cutting short his trip.

Ban's visit comes as millions of Pakistanis are increasingly frustrated by the government that has already been hit by political bickering.

Flood victims have complained that not enough government aid is arriving and looting has occurred in many flood hit areas amid increasing signs of lawlessness.

Pakistan's government has been accused of being too slow to respond to the crisis with victims relying mostly on the military and foreign aid agencies for help.

"New threats"

Charities said relief for those affected by the disaster, which has left more than 1,600 people dead across the country, was lagging far behind what was needed.

"There are millions of people needing food, clean water and medical care and they need it right now," Jacques de Maio, head of operations for South Asia at the International Committee of the Red Cross (ICRC), said.

Floodwaters pose new threats to the populous Sindh province and the southwest province of Baluchistan, a region also hit by a decades long separatist insurgency.

In the northwest Swat valley, flour, cooking oil and rice were carried by mules along narrow mountain tracks to 150,000 people in Shahpur, with roads cut off and the weather too bad for helicopters.

The United Nations has warned of a second wave of deaths among the sick and hungry if help does not arrived.

Cholera, which can spread rapidly after floods and other disasters, had also been detected in the northwest, where the floods first hit more than two weeks ago after exceptionally heavy monsoon rains.

The U.N. has reported the first case of cholera amid fears that disease outbreaks could spread with survivors sleeping in makeshift tarpaulin tents. Some beg or loot.

Bridges have collapsed, highways have been snapped in two by torrential rains and villages have been cut off from the outside world in what was already one of the poorest countries in Asia.

The International Monetary Fund has warned of major economic harm and the Finance Ministry said it would miss this year's 4.5 percent gross domestic product growth target.

Any economic downturn would come just as the government aims to fund projects across the country to win hearts and minds in the battle against the Taliban.

Wheat, cotton and sugar crops have all suffered damage in a country where agriculture is a mainstay of the economy.

Agencies