Sea surges have devastated a wide stretch of Sri Lanka's eastern coastline, including popular tourist beaches in the south. Thousands are reported dead and more than a million people have been forced from their homes.
Eyewitnesses to the disaster wrote to the BBC News website about their experiences.
Sri Lanka is perhaps the least prepared to cope with a disaster of this magnitude as a result of the massive floods that struck the country only a few weeks ago. In some parts, the civil war hasn't helped either. For example, the tidal waves have uprooted thousands of landmines in war-torn regions, making rescue efforts dangerous and inaccessible for the neediest. However, the damage is widespread - north to south, east to west. As I write this, I can hear an old lady crying on the phone to inform her relatives abroad about the deaths in their family.
Justin, Colombo, Sri Lanka
Thank the Lord that I am safe in Sri Lanka despite all the catastrophe happening here. We were at the beach when it happened - we were told not to go into the sea because a tidal wave had come in. I thought that only meant that the tide had come in and would go out as the day went by. I did not comprehend the full danger of tidal waves and wanted to stay and see how far the water would come up. A friend had better sense and insisted we leave. It was eerie driving away from the coast as people streamed towards it, likely to see what was happening, the radio news announced what had transpired but it was only when I saw the full extent of what had happened on TV that I understood the magnitude of the destruction caused.
Judie, Toronto, Canada
I was finally able to talk to some people in Bentota, on the south-west coast of Sri Lanka. All the tourist hotels, the railway station in Bentota have been destroyed/damaged. Hotels were packed with tourists. Many have drowned, injured, though numbers not known. Estimates of foreigners injured etc currently given are probably highly underestimated. I understand that a train load of people were swept away. The country needs a massive amount of help even to get back on its feet.
Wijit Dharma, Edmonton, Canada
My cousin Mr Daya Ranjan Wijaya Gunawardana was a passenger in the train that was washed off at Hikkaduwa, Sri Lanka. His compartment was filled with water and turned around four times before it landed. When he scrambled out with great difficulty he found his grown-up son and daughter, who were travelling with him, also clinging to the side. Amazingly, they are fine, except for body aches.
Dr Upul Wijayawardhana, Grantham, UK
I was jogging in the early morning when, with a huge noise, the waves came in and covered the entire area with water. Shops and small houses collapsed and people were running all over to find a safe place. Some were trying to carry their belongings with them. Many people are displaced and the armed forces are trying their best to help the people who are affected.
K Prasanna, Colombo, Sri Lanka
I'm emailing from an internet cafe across the road from our hotel, Browns Beach in Nygombo. Sitting on the beach terrace having lunch, I saw an enormous wave heading for us. We all jumped up and ran - all we could hear was breaking glass and screams. It was chaos, people were injured by spraying glass and some had to be taken to hospital. The ground floor of the hotel is devastated, as are all the beach bungalows. The hotel staff are amazing, having food brought in, looking after the guests. Travel agents have not even been in touch, we have not a clue what is happening about being re-housed. There are no hotels free, they are all booked up. At least 50 families in the hotel have lost luggage drifting out to sea. It really is bad here. People are praying in the churches, the locals are all leaving town.
Jacqui Walker, Sri Lanka
The tsunami has caused inconceivable damage in Sri Lanka. The extent of the damage can be visualised by the following facts - a train with 1500 passengers was washed away, all passengers missing, buses are seen floating in deep sea with no clue of the passengers on board, some villages, hotels and markets have washed away leaving no trace.
Harshana Somapriya, Moratuwa, Sri Lanka
Huge tidal waves hit many different coastal areas here in Sri Lanka. The most devastating tides were seen in Muttur and Trincomalee and the death toll is nearing four figures. Witnesses are bewildered as to how fast everything happened. One moment they saw the sea water rise to heights of around 20-feet and the next moment it was as calm as ever. Some parts of Colombo have also seen minor waves entering the shores, some hitting the rail roads and bringing down shanties. This is the first and worst we have ever seen.
Mohamed Mohideen, Colombo, Sri Lanka
I would like to express my gratitude to the people of Sri Lanka. When the wave hit our hotel not one member of staff fled in fear, instead they helped us. The manager himself was washed away by the wave but he surrvived and then came back to make sure all his guests got out safely!
Whilst their country reaches new levels of tragedy hour by hour the people selflessly evacuated us to safety in Colombo and then relentlessly looked after us until we got flights home.
I feel that I owe the staff of my hotel my life. Thank you all!
Deana, Swindon, England