Beneath the crumbling arcade of the municipal council building in Beira, in Mozambique, a group of families has set up a dismal camp. They sleep on dirty concrete pavement and cook with branches from the trees brought down by Cyclone Idai which swept through southern Africa last week.

Winds of more than 100mph triggered devastating floods and more than 400 people were killed, according to government sources. Land and environment minister Celso Correia said that the situation in the country was now critical.

Laila Jorge, a mother of three, was one of those caught by the storm. A street vendor of alcoholic drinks, she was living in Zona B, a poor area of the port city of Beira, where shacks were once located close to the sea. “When the wind came, it took off the roof and blew down the wooden walls of my house. We had to run because we thought that we were going to die. There was waist-deep water [from the storm surge] in the street, so we ran here. We didn’t have our shoes and our feet got cut from glass we couldn’t see. We stopped when we got here because it was dry and because it was empty.”

Jorge and the others have lost everything, she added. Her pots and flipflops were donated by workers cleaning up the damage and who took pity on them. Apart from that, they have received no aid.

Near Jorge, several children are gathering water in large plastic bottles from a deep puddle that has overflowed from the fountain pool in the square opposite. Next to them, a boy of about eight is washing tiny sprat-like fish that glisten in a pot. Jorge said the fish were washed up by the cyclone and stranded in the pools of standing water left in the city and were now being collected by local boys. “Dead or alive, we’ve been eating them,” she said, “because it’s all we have to eat.”

Jorge said dirty water being scooped up and carried by the children from the square was for cooking and washing, not drinking, but added that her children aged three, five and seven all had diarrhoea.

Despite a huge global-aid appeal that has raised tens of millions across the world, including in the UK, many like Jorge have yet to see assistance. For their part, international aid officials have admitted they were initially blindsided by the nature of the catastrophe. They had focused their initial efforts on Beira, which the Red Cross initially thought was largely destroyed by the cyclone. They did not foresee the arrival of devastating floods that would hit huge areas of the countryside more than a day later.

Facebook Twitter Pinterest Locals waiting to be rescued after floods hit huge areas of the countryside. Photograph: Andrew Renneisen/Getty Images

That wrongfooting had consequences. Badly needed helicopters, required to rescue people in the countryside sheltering in trees, on roofs and in electric pylons, were slow to arrive. “We could see from our first aerial surveys that Beira had been badly hit,” Jamie LeSueur of the Red Cross told the Observer. “What we weren’t able to predict was the scale of the flooding that would follow.”

Even now officials admit they have yet to get a full picture of the scale of the disaster. They merely describe it as “overwhelming”.

And the biggest impact may be the least visible in one of Mozambique’s most densely populated regions. After several years of drought in southern Africa, the subsistence farmers who populate the coastal plains have lost their crops at harvest time. They have no food or produce to take to market.

This weekend emergency efforts were shifting from search and rescue – led by the pilots and boat operators who have plucked people from the floods – to humanitarian assistance. Within the next few days a road route will reopen to Beira, ending the bottleneck on food supplies.

Helicopters, badly needed to rescue people sheltering in trees, on roofs and in electric pylons, were slow to arrive

And as the waters have started to recede, the number of those wanting to be evacuated by boat has begun to dwindle, with many preferring to stay put or relocate to the expanding dry areas closer to their homes.

“We hailed people from our boats,” an Indian naval officer involved in the rescue effort told the Observer, “but most of those we saw wanted to stay where they were.”

The United Nations Office for the Coordination of Humanitarian Affairs (OCHA) said yesterday it would have to wait until the floodwaters recede until it knew the full expanse of the toll on the people of Mozambique, while the International Federation of the Red Cross and Red Crescent Societies (IFRC) warned that cases of cholera have now been reported in Beira.