Torrential rain has battered makeshift camps in Haiti, swamping earthquake survivors in mud and giving a menacing foretaste of the coming rainy season.
Thursday's downpour soaked shelters made of bedsheets that are home to hundreds of thousands of people in Port-au-Prince and added urgency to the race to supply tents and plastic sheeting.
Aid agencies and the Haitian government warned of another humanitarian disaster if adequate shelter and sanitation did not arrive before the rainy season - which is expected to start between March and May and continue until autumn.
The warnings came as the UN increased its relief appeal for Haiti to $1.44bn (£929m), bigger than the previous record of $1.4bn after the 2004 Asian tsunami.
"As the rainy season is coming to Haiti, it will be extremely important to provide on a priority basis shelters, sanitation and other necessary humanitarian assistance," said the UN secretary general, Ban Ki-moon, announcing the new total. With more than $600m already pledged in the immediate aftermath of the quake on 12 January the outstanding target was $768m, he said.
The magnitude 7 quake levelled much of Port-au-Prince and killed 230,000 people, according to the Haitian government. About 500,000 survivors are sleeping rough and another 500,000 are crowded in several hundred makeshift camps.
Bill Clinton, the UN's special envoy for Haiti, urged people to donate immediately. "Pledge less and give it. And do it sooner rather than later."
It is feared that rain will turn camps into quagmires, trigger mudslides and spread disease. "We need latrines, we need field tents, we need plastic sheets so that people can cover themselves," said the UN's top official in Haiti, Edmond Mulet. "I don't think we are going to be able to shelter all these people in time."
Rather than tents, some aid agencies prefer durable plastic tarpaulins which can be suspended on poles and later be used to line huts. The UN is trying to distribute tarpaulins to up to 1,500 families daily. The hope is that families will have two tarpaulins each by 1 May.
A group of American senators sent a letter to the US president, Barack Obama, this week urging the immediate relocation of Haitians who have camped in gullies and at the bottom of hills. "Tragedy will strike again when the rain comes," they wrote.
Several aid agencies are frustrated that Haiti's authorities have not followed through on talk of new campsites. The UN humanitarian chief, John Holmes, had privately criticised the aid effort, but the Haitian president, René Préval, said the government was focused on shelter.
"Every time I meet with foreign leaders and delegations, I tell them that is the most urgent need. Now that we've attended to the wounded, taken away the dead, and we're distributing food and water, the problem of shelter, the tents, is the most urgent," he said.