A Christmas tree with tinsel lies forlornly on the ground with what looks like small presents scattered around. Next to it, a table is laid out with plates, food and cutlery as though the family is ready to come back for dinner. I can see all this clearly as the front wall of the house has exploded and pushed out onto the street, exposing the family dining room.

It has been like this for the last three days. Whether the inhabitants of the house, surrounded by collapsed buildings and debris, will ever come back is quite another question.

The scenes in the streets of Port au Prince, Haiti, since the earthquake hit on Tuesday are ones of confusion, panic and despair. Shocked, bleeding people covered in grey dust wander around like ghosts, frantically searching amongst the rubble for loved ones or seeking transport to hospital for wounded family or friends.

All the hospitals are full and understaffed - many of the city's medical personnel have been killed or injured in the disaster - with only one facility still treating the sick and dying. A small number of those hurt were able to seek medical help across the border in the Dominican Republic. Others had no choice. Their bodies pile up outside the hospitals and in the streets of the capital. But with body bags running short, corpses are lying open to the elements or wrapped in sheets and cardboard in the hope that the authorities will pick them up. The UN has started to clear them away, but still the smell of death pervades, and people are forced to wear masks to keep it at bay.

As you will have watched on the TV, the monuments of government have been razed to the ground. The UN Mission's HQ and some of Pétionville's most luxurious mountaintop hotels have been flattened. When you see that, you know that the shanty huts, which once stood flimsily stacked like cards on the side of hills, didn't have a chance. Nor did the people in them.

The death toll from this latest disaster is impossible for us to measure or understand, but it is thought to be 100,000. Over three million people have been directly affected, losing family and friends and left without enough food, water or shelter to survive. Oxfam's immediate priorities are to provide safe water and shelter material for the people who have lost their homes, but given the scale of the effort and the fact that this catastrophe has wiped out all the city's infrastructure - the foundations needed to co-ordinate an aid response - it's not been easy. Our warehouse in Haiti was hit and stock badly damaged. We are using the contingency supplies we managed to rescue, but we are in desperate need of more. Fuel is running out and we have no electricity and scant communications.

In the immediate aftermath, Oxfam has been providing shovels and picks to local civil staff to clear debris to help search for trapped victims, but bodies have been lying under the rubble for a long time because it is difficult to access some sites and heavy lifting equipment is in limited supply.

Impromptu camps are springing up around the city. Survivors are sleeping open air on the streets, on football pitches and in any free space, too scared to go into buildings still standing for fear of aftershocks. Others have fled to the countryside in search of better conditions, but as communications are non-existent, we don't know what awaits them there and with the aid effort concentrating in the city, this concerns us.

We understand that the government plans to create 14 sites around the Port-au-Prince to give people somewhere to sleep. In this situation, camps could offer the best temporary solution to get food, water and sanitation to those in need. There has been no rain yet, but there was rain earlier in the week, and if it comes again, it will make the situation much worse for all those made homeless by this quake.

People are resilient and helping others where they can, but due to their desperation and the concentration of survivors in large numbers in small spaces, there has been some looting and outbreaks of violence.

Haiti was already the poorest country in the western hemisphere before this disaster struck, with 85 percent of its inhabitants living on less than two dollars a day. On a good afternoon, it wasn't easy to move about in Port-au-Prince, its tight, twisty, rutted roads and tracks difficult to navigate. This disaster comes just 16 months after four hurricanes killed 1000 people, leaving hundreds of thousands homeless and causing an estimated $1 billion dollars of damage to infrastructure and agriculture. This country and its people aren't fit for this.

Our 100-strong squad in Haiti is experienced in dealing with emergency situations and they dealt with the fall out after the recent hurricanes. But they too are struggling to cope with the loss of their homes, family members and colleagues, while trying to help others.

Like so may other of the aid agencies co-ordinating this response, our Oxfam office in Port-au-Prince collapsed and I am sad to report that one of our team, Amedee Marescot, has died as a result of his injuries. But everyone is trying their best to get aid in and help the most vulnerable. And it is arriving and scaling up.

Yesterday (Saturday), we managed to set up two bladder tanks in the city, which allow us to distribute 10,000 litres of clean drinking water, one at Delmas 42 - a former golf course, now home to about 10,000 displaced - and another at a hospital in one of the worst hit areas, Carrefour.

These came from existing stocks in country, but more are desperately needed. With the help of the generosity of the Scottish public, in the early hours of this morning (Sunday), ten tonnes of Oxfam water, sanitation, health and shelter equipment arrived from the UK to Santo Domingo in the next door Dominican Republic, including chlorine for drinking water treatment, buckets, plastic sheeting and, tragically, more body bags. Our warehouse in Panama is also on stand by to send more stocks.

Seventeen Oxfam humanitarian experts have also been drafted in, amongst them John Kerr, a logistician from Edinburgh. They will help co-ordinate the aid's distribution and make sure it gets quickly to those who need it most. We are expecting another flight from the UK on Tuesday and one more next Friday.

Despite their grief and the challenges on the ground, the Oxfam staff in Haiti are working flat out to make this operation a success. Amedee would have wanted us to keep going and get aid to the survivors, and in his memory, and in memory of the others who have died, we are doing exactly that.

How you can help

The Disasters Emergency Committee in Scotland - made up of the main aid agencies including Oxfam, Christian Aid, British Red Cross and Concern - has launched an appeal for funds.

You can donate by visiting www.dec.org.uk by calling 0370 60 60 900 or text "GIVE" to 70077 (donates £5 to the DEC for Haiti. (UK only))

* £10 can buy 6 buckets to help families get access to water

* £15 can buy a hygiene kit with essentials such as soap, detergent, toothpaste, toothbrushes

* £20 can buy three tarpaulins or plastic sheets to provide basic shelter to protect families

* £25 will supply a kit of household essentials

* £50 buys a food pack to feed a family for a fortnight.

* £100 provides temporary shelter for two families.