The World Food Programme has started its first systematic food distribution system for Haiti since the earthquake, with 16 sites set up in the capital where only women may collect food.

Food distribution since the quake on 12 January has often been marked by poor co-ordination, gaps in coverage and desperate, unruly lines of needy people in which young men at times have shoved aside the women and the weak and taken their food.

The UN agency said in a statement that the fixed sites established across Port-au-Prince will ensure a regular flow of food and other humanitarian assistance to all those in need.

Download the new Independent Premium app Sharing the full story, not just the headlines

News that food aid was finally getting through came as the US military suspended the airlift of critically ill people to American hospitals, pending the resolution of a dispute over who would pay for their care.

One doctor, Barth Green of the University of Miami, last night said his team had "100 critically ill patients who will die in the next day or two" if they were not flown out. They included a five-year-old girl with tetanus from a minor leg wound, who Dr Green said would die within 24 hours without a respirator. Earlier this week the Governor of Florida, Charlie Crist, wrote to the federal government asking for financial help. His state's hospitals had already treated 436 seriously injured Haitians and were "reaching saturation", he said.

Back in Haiti, people have started receiving coupons entitling each family to 55lbs of rice. The first distributions begin today, with only women allowed to collect rations. The World Food Programme said it would work to ensure men in need are not excluded. It aims to reach more than two million people in the next two weeks. So far, it has dealt with about 600,000 people, supplying more than 16m meals.

The agency said the collapse of Haiti's infrastructure, losses in the aid community, security concerns and the huge scale of need have hampered their response. The executive director, Josette Sheeran, said the emergency was "the most complex challenge we have ever confronted".

Few tents have yet been supplied to survivors, rubble has yet to be cleared, and signs begging for help in English – not Creole – dot nearly every street corner in Port-au-Prince. Haiti now has fewer than 5,000 donated tents, but needs 200,000. Getting these could take weeks, said Marie Laurence Jocelyn-Lassègue, the culture and communications minister.

Yesterday, Gordon Brown announced that the Government had bought every single piece of corrugated iron in Britain and will be sending it to Haiti to create shelters.

Reconstruction, resettlement and land titles are all priorities of President René Préval's government – so far in name only. It has been nearly paralysed by the quake – its own infrastructure, including the National Palace, was destroyed – and so far all it has done is make appeals for foreign aid and attend meetings with foreign donors.

Many people who have tired of living in tents improvised from tarpaulins, sheets and bedspreads have opted to rebuild their homes rather than find new plots. But Ms Jocelyn-Lassègue has said this will not be tolerated – the government wants to develop a comprehensive reconstruction plan that features proper building regulations.

"We've been sleeping outside, but the rains will come soon," said Merilus Lovis, 27, taking wooden planks and erecting them for walls inside the foundation of his former home where his wife and daughter died.

Others have swarmed to improvised tent camps, where Elisabeth Byrs, an official with the UN Office for the Coordination of Humanitarian Affairs, said there is a "major concern" about sanitation. About 200,000 people are in need of follow-up treatment after surgery and an unknown number have untreated injuries, she said.