Chaos reigns on the streets of Port-au-Prince, with machete-wielding mobs forming roadblocks, and people looting whatever they can lay their hands on.

People are visibly angry and baffled at the inability of foreign governments and major international organisations to come to their assistance quickly enough. UN peacekeepers may struggle to keep the peace, with around 4,000 convicts let loose after the prison was destroyed. Up to 10,000 US soldiers are set to deploy to Haiti over the coming days, to try maintain law and order, and help relief get through.

But the capital's already-rickety infrastructure was pulverised by the 7.0 quake, in turn throwing sand in the cogs of the international aid operation. The seaport destroyed, the US military took over at the international airport on Friday, but the backlog of flights meant that relief workers and supplies struggled to enter, four days after the earthquake. Sitting in Miami Airport on Friday afternoon, the departure screen listed numerous commercial flights on the regular schedule to Port-au-Prince, but all were labelled as cancelled.

Goal staff had to get to Jamaica and jump on a Digicel jet, to reach the stricken Haitian capital, where they will partner with Haven to help the stricken. Irish telecoms company Digicel has operated in Haiti since 2007, and with its US$5m provision, is to support relief work.

But when Digicel's flights were caught in the backlog, Goal emergency co-ordinator Brian Casey flew to Santa Domingo in the Dominican Republic, the other half of the Hispaniola island alongside Haiti. From there he made a six-hour road trip to Port-au-Prince, via rioting mobs in the city who are growing increasingly angry at the hamstrung international relief response.

"The city is destroyed and the people are becoming increasingly desperate," he said. "Everyone here is touched by this disaster, having lost loved ones. People are getting angry, they need medical supplies, food, water – or there will be another disaster here."

Now the road in from Santa Domingo is slowing to a crawl, with 12-18 hour journey times being reported, as some aid for Haiti is being routed through the Dominican Republic.

All over the city, what were once buildings lay in heaps of broken concrete, steel and dust. Everywhere, dust, and government buildings slumped in the distance, like giant heaps of white plaster sitting under the morning sun. Everywhere, cinder blocks were ground into powder as they collapsed, with little sign of steel-fixings to reinforce buildings.

Shoddy construction has added untold numbers to the death toll. I remembered the words of a specialist earthquake engineer I interviewed in Kashmir, while overlooking the wreckage of the Pakistan earthquake in late 2005. He said: "Earthquakes don't kill people, buildings do."

And now, as we have seen so often elsewhere Port-au-Prince is a reminder that it is the least well-off and poorest governed countries that suffer the most when disaster strikes.