More than 130 partygoers were packed on to the Marchioness pleasure boat cruising along the River Thames on a warm August evening in 1989.
As they danced, the boat was hit by a 1,880 tonne dredger and sank within minutes - 51 people were killed.
On the 20th anniversary of the tragedy, one of the survivors and a bereaved mother describe how their lives were changed that night.
Ward Bingham, from Vancouver, Canada, was 23 when he lost 13 friends in the Marchioness disaster.
It was a wonderful evening in London. It always looks beautiful at night but from that vantage point on the river you could see everything. I was outside, so was able to see the accident happening. I was lucky, as it allowed me to have an escape plan.
When we went through the bridge, suddenly there was this huge wall of blackness just looming down on us. I looked up higher and could see two lookouts on the front of the Bowbelle, looking down on us and yelling for us to get out of the way.
I made eye contact with them. Then suddenly the boat hit us. The record which was playing skipped and everyone sort of went, "whoa, that was kind of fun".
Then it hit again and the Marchioness began to tip on its side. Because I was outside I knew very well this wasn't looking good.
As the boat began to tip, the passengers who were standing on the far side began to slide down on top of me and I had to climb out.
There was no time to think about grabbing anyone, it just became mayhem and at that point I had to jump. I knew I couldn't just swim away but had to go to the bottom of the river while the boat went over me.
When I was down there the noise of the boat was coming around me and people were grabbing on to me. It was horrible, horrible. I was coming close to death, I was becoming comfortable with the idea that this might become the end of me.
I was a very strong swimmer, I managed to swim to the side and tried to flag down passing traffic.
I heard people screaming from the other side of the river, then helicopters and ambulances started to arrive. Whenever I hear a helicopter it always takes me back to that moment, it just frightens me so much.
So many things in life, almost on a daily basis, will take me back to that moment. You learn to live with it but you never get over it.
I went to St Thomas' Hospital, where a lot of friends had been taken in ambulances. Some were standing around but a lot were missing.
One of my very close friends, Peter Alcorn, died. He wasn't found until 12 or 13 days after the accident. I had to go and identify his body. It was unbearable.
His family was back in Nova Scotia and I had to go and pack up all of his stuff. I remember standing in his room, looking at everything and just bawling, packing up his stuff and going through his life.
The problem was, the friends who survived were just as messed up as me. So being able to turn to friends who you would normally turn to, these people had died or were going through the same thing.
We really didn't have any support, no-one who could help bring us back up. We were all in our early or mid-20s, young, young, people and this was such a big thing.
We were all very creative people, all had budding careers. I was a shoe designer, but I lost all of my creativity after the accident. I turned in a very dark direction, had suicidal thoughts. What had given me so much joy was gone.
I went from being a shoe designer to selling cleaning products on a market. My parents had to support me financially. My life was no longer recognisable, I didn't recognise my friends.
We were studied by Middlesex University and they compared us to Vietnam veterans, as we had lost a lot of friends and were going through the same thing at the same time.
I'm now happy but it's taken a lot of work, I've been through a lot of therapy. It took me a long time to be able to develop friendships again, as those friendships were ripped away from me.
What's really helped is starting my business, mondonation.com. I wanted to create something which would give something back and we support a lot of charities.
I now feel I have to let people know that as much as you go through in life, you can get through to the other side.
Margaret Lockwood-Croft lost her son Shaun, 26, in the accident. She fronts the Marchioness Action Group which represents the victims and campaigns for improvements in river safety.
We have got a lifeboat service now and there have been improvements not only on the Thames but on all UK waterways.
It is reckoned the lifeboat service has saved 276 lives since it was brought in. It makes me think about all the other lives that might have been saved if the service had been introduced earlier.
I think of it as a legacy of love for all of those who were lost and the survivors. It's enormously sad that 51 people had to die for it to happen. But quite often someone has to lose a life before change occurs.
I can't even begin to describe the loss when you lose a child like that.
What started it was they wouldn't allow me to see my son, but then I found out that no-one has the right to deny you that. I started looking into other areas. I wrote to the other families and survivors along the way to make it more powerful and they would vote on things. We all had an impetus that way.
It was the only way I could cope personally with the death of my son, otherwise I would have shut myself in a room.
He was an outgoing, bright young man who would not have liked it if I had lived in that way. I never thought it would take all these years to achieve. In many respects, fools rush in where angels fear to tread, but I didn't want to give up.
My mother said it wasn't just a grandson she lost that night but her daughter as well. She said there is a sparkle that is not in my eyes anymore. I look at the survivors' experiences and it's had the same effect on them. They didn't only lose friends and colleagues that night, but something else.
It took four months before I could start dealing with my son's property. Going back into the room he had left, the cup of coffee left on the counter, he was due to be going on holiday in a few weeks and there was a list of what he was going to do.
I've got a suitcase of his in the loft which I've never had the courage to part with.
I've looked back at old diaries this year. I wrote down about how he came down one night and when we were chatting away he wanted to know about my beliefs. We were laughing because it was 5am and we could have had breakfast as we had been up all night.
He said he believed it didn't matter how you live, it's how many hearts you touch and how many lives touch yours when you go. I wrote it down. By August he was gone.
He'd written a will and written a letter to me which I found when I was sorting through his things.
Everyone deals with grief in different ways. The journey you make is a singular one. The only way I could survive was to leave a legacy of love and to work to change attitudes, procedures and laws.