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 have said.
BBC News website readers around the world have been talking to the BBC about their search for missing friends and relatives. Here are some of their stories.
KATHY JOHNSON, READING, UK
We are desperately worried because my uncle Pierre Celestin and six of his children are missing in Port-au-Prince.
The area is devastated. The church and graveyard where my grandfather is buried has been destroyed and I am stuck here thousands of miles away.
I feel so frustrated, all I want to do is to jump on a plane and go to help
I feel so frustrated, all I want to do is to jump on a plane and go to help.
I have several family members in New York, and they are not coping well. My aunt is going out with the Red Cross to help, and hopefully find them.
We have to believe that my uncle and as his sons are still alive.
I've been constantly trying to phone through to Haiti. I am doing everything I can to try to gather information - I'm on Facebook and Twitter all the time. Someone, somewhere must know something about them.
When the earthquake struck I felt so alone as there are so few Haitians here in Britain. I have joined the group
in the UK. We hope to raise funds and help in any way we can. I just want to appeal to anyone in this country to give any help you can.
RUTH NORBURY, BRISTOL, UK
My husband is from Haiti and has a large family that live in Carrefour, on the edge of the capital Port-au-Prince.
It must be a miracle because although the houses around them are broken, all eleven of his relatives are still alive and uninjured and their house is ok too.
We feared the worst when we saw the pictures on the news. It was 3am yesterday when we heard. We didn't get much sleep after that.
All the reports from Carrefour were of houses that had been flattened. The place had been "levelled".
We tried to get through to the family. The phone lines were down, the internet was down. It was just a case of constantly trying, but we couldn't get through at all.
Getting through the day was difficult. All we could do was watch TV and look out for people we knew.
When I got home at nine o'clock last night I finally heard the good news.
My husband got through to his younger brother on the phone. He said: "We're fine - in fact none of us have a scratch."
Eleven members of the family were in the house at the time of the earthquake. But they all survived. And the house is intact. Even though everything was in tatters around them.
All I can say to people is don't give up hope just yet because among the darkness sometimes there is a small glimmer of light.
I hope more families will have good fortune like we have.
LANDON YARRINGTON, PORT-AU-PRINCE, HAITI
Earthquake damage in Haiti. Picture: Eric Lotz, Operation Blessing
My partner and I are US citizens who have been helping in the triage areas of the main UN base near the Toussaint L'Ouverture airport since the night of the quake. We are civilians and are still waiting to hear word back from officials in the US Embassy about evacuations. Until then, we're here comforting families and children and doing whatever we can to help the incoming victims.
The UN is supposed to begin building a new mobile hospital today. Around 2,000 US marines are supposed to land as well. The UN has already sent out wounded foreign nationals to hospitals in Miami, along with very badly wounded Haitians. Two Haitian girls are waiting for foot amputations sometime today. Our passports, computers, clothes and medicine are all buried in the house we were staying at in Port-au-Prince. All that we have with us now are the clothes on our backs.
We were talking with friends in an adjacent neighbourhood when the quake hit. We immediately walked back to our friends' house to find that that everyone was mercifully OK. Afterwards, we began rounding up all the wounded from the surrounding neighbourhoods and put them all in one area. We gathered together more than 200 wounded and the message kept spreading.
Tremors still shake everyone in the compound and make it especially difficult to get any sleep at night. These past two days have been a nightmare, especially for the countless Haitians who have lost everything.
BARBARA JONES, MILTON KEYNES, UK
I am Haitian and have lived in the UK for just eight months. I was working and living in the Dominican Republic before then and if I was there now, I would have run across the border to find out what has happened to my family.
I have not heard from my mother or my cousins. My aunt is also missing. She gave me my education and I owe her so much, she was a huge part of my childhood. My family live in Port-au-Prince, right at the epicentre of the earthquake. I haven't heard from any of them.
I have been calling all my other relatives and friends in Haiti. The phone lines are down a lot of the time and I can't get through. I am relying on family in America as well.
I am recently married and my husband has been wonderful. He has been supporting me otherwise I would be feeling very alone.
Haitians, we are used to disaster but this is the worse thing that has ever happened. Everything is destroyed. It is so upsetting.
Haiti's government cannot respond to something on this scale. To see how the whole world is responding is amazing. I am close to tears when I see how everyone is coming to help us.
SEBASTIEN BARRAU, MIAMI, USA
Sebastien Barrau and Marvin Chery
I am from Haiti and I moved to Miami four years ago. My family is still there. I got a call from my sister asking me to call her back straight away, she mentioned something about an earthquake. I didn't think it was that bad. When I got off the phone to her, I checked Twitter and I could see everybody posting information on there.
I started to get really worried for friends and family but it was my first day at a new job so I felt I couldn't just get up and leave. It was so terrible seeing the images on the television and online. Places I know and have visited were just destroyed. Haiti has had a lot of problems but nothing like this.
It's so shocking to see how everything has been destroyed and I just want to go back and help. I can't though and so I decided to create a
to help. I had a lot of people on Twitter contacting me, asking for information about loved ones. I thought it would make sense to get a website together where people can put up pictures and appeal for information about missing people. Everybody is worried and the list makes it easier. My school friend from Haiti, Marvin Chery, and I put the website together and it's now live.
I'm really disappointed. There are so few survivors. I spoke to a friend who helped get five people out of a collapsed supermarket, just five people. I've heard about people being alive one day and stuck under the rubble but who don't make it.