Up to 10,000 US troops will be on the ground or off the coast of Haiti by Monday to help deal with the earthquake aid effort, US defence officials say. It is feared thousands of people have died in the earthquake.
BBC News website readers have been describing how the earthquake has affected them.
JENNY REITZ, LA POINTE, HAITI
We run a home for sick and malnourished children and we're based in La Pointe, a small town outside the city of Port-de-Paix on the North Coast of Haiti.
Many of our children study in Port-au-Prince which is 150km away. We have been spending the day trying to find out if they are still alive and if they are we are trying to get them back here. We have good friends and family around us but it has been incredibly stressful trying to get information.
Many families, if they have the money, will send their children to school in Port-au-Prince. There were five children that we were specifically trying to get hold of and I have also been trying to find out information on a further 50 children from local families.
I found out today that thankfully they are all still alive. They are all in their 20s and studying at university. Every single one has lost their accommodation in Port-au-Prince. They have been living on the streets, trying to find food and water to survive.
From the other 50 local children we have been trying to trace, some have made it back. They have had terrible experiences; watching their friends die in front of their eyes.
Others have made it back. The whole town is going through mourning. Every couple of hours we hear of someone who hasn't survived.
Even though we are 150km far from Port-au-Prince, in a country like Haiti we depend on the main supplies lines from there. That line has now been cut and I think we can expect to see food, fuel and basic supplies dwindle over the coming days.
BARBARA JONES, MILTON KEYNES, UK
Update from Barbara, a Haitian who has been in the UK for eight months
One of my relatives in the US managed to speak to a member of our family in Haiti. She got through by chance on the phone, we had all been trying since the earthquake happened.
She said my aunt and my cousins are OK. They are now living in the street in Port-au-Prince so they won't get hurt by falling buildings, but at least they're OK.
We still don't know about my mother. She lives outside the capital, in Gonaives which was badly affected by hurricanes in 2008. It's even hard to get hold of her at the best of times.
ANDREAS DITTMER, GERMANY
My wife, Mimi, is stuck under the rubble of a supermarket in the Delmas area of Port-au-Prince.
On Wednesday we heard that Mimi had managed to use a blackberry phone to text her cousin in Haiti. I haven't been able to talk to her to confirm this. I've also heard that someone managed to speak to Mimi on Thursday, at the time she was stuck with another 25 people. But I just I don't know whether this is true.
What I do know is that her car is still parked at the supermarket.
From talking to rescue teams, I'm hearing that there are possibly 50 people in the rubble there. It's difficult to get to them because of the lack of heavy equipment - the ceiling of the supermarket is just too hard to break through, and there aren't enough rescue dogs in the area either so the rescue teams don't know exactly where to dig.
I'm hearing many conflicting reports from Haiti and we're powerless to do anything. I feel desperate.
PAUL BERTONI, PETIONVILLE, HAITI
People have been sleeping in the street.
I live in the Dominican Republic but came here soon after the earthquake to look for my relatives. I am in Petionville. It is probably one of the least affected areas of the city. I have been driving in the streets all day, trying to find friends, relatives, looking for food, water, fuel, taking pictures.
The streets of Port-au-Prince are filled with dead bodies covered in sheets. It looks like the entire city structure is collapsed. There is still no phone communication, no electricity, no public transportation.
People stay and sleep right in the streets. Some have no houses to go back to, some are afraid of another quake.
There is no kind of rescue from the public services nor the humanitarian aid. People are trapped under the rubble and slowly dying.
The air is starting to smell like dead bodies. People are wearing masks as they walk the street.
The population is extraordinarily calm and quiet. Still stunned by the magnitude of the blow.
A lot of people are going up and down the street. I imagine they are looking for resources, looking for their relatives.
At around 10pm last night, a neighbour of a relative we went looking for asked us if we could help him get his 13-year-old son from under the rubble. He said he had managed to pull out his three daughters, but not his son.
He pointed to a spot under the rubble and asked me if I could see the boy's hand. There were three little fingers in the middle of the concrete and the metal. I said I couldn't help.
He asked if I could broadcast the news that his son was dead on the radio, so that the boy's mother could know, as she he was not at Port-au-Prince at the time
JOEL DRESSE, MIAMI, US
I live in Haiti but was on a business trip to the United States. I am trying to go back to Port-au-Prince to reunite with my parents. I am flying to the Dominican Republic and will then go to Haiti by taxi. It will take me from eight to nine hours.
My parents live very near to the Caribbean Supermarket which fell down in Petionville. I managed to talk to them after hundreds of attempts over the phone.
They told me there is no water or food. They took around 200 neighbours into the house and they are sleeping by the swimming pool. They can take water from it and boil it and use tablets, but there is almost no food. My mother says she can still hear people crying for help.
We are bringing 200 pounds of dried food with us, but that cannot possibly feed 200 people.