Here is a selection of eyewitness accounts we received from people involved in the explosion between King's Cross and Russell Square.
We had just got through King's Cross when I heard an almighty 'boom, boom' and the carriage stopped immediately. The electricity went completely and the carriage filled with soot.
We could just make out what was in front but nothing else.
The explosion was on the ceiling of the carriage in front and all the glass from the carriage had caved in.
People were trying to kick the windows in.
I could see there were people with their clothes burned off, people with limbs missing.
Ian Wade said he had "never experienced anything like it"
There must have been at least one death in there.
I have never known anything like it.
My wife Evie really thought that we were going to die. It was just 'boom' and that was it. I couldn't think straight.
When the emergency services arrived, we all had to walk through the carriage in front to get out.
Luckily there was a lot of straight thinking people on the Tube - there was only a few people who were losing it or screaming, but they were in the carriage where the blast happened.
I don't know what to think. I've lived in London all my life and I've never experienced anything like this.
I was on the train between King's Cross and Russell Square.
There was a loud bang just about 100m [328 feet] out from King's Cross.
The carriage filled with thick black smoke and plunged into darkness briefly.
A few people freaked out but generally everyone was calm thinking it was a power surge.
I had no idea that it was a terrorist attack.
We evacuated out the back of the train about 30 minutes after being trapped.
The smoke made us think it was a fire at first but then the smoke didn't seem to increase and people thought it was just dust thrown up by the blast.
The carriage was packed and claustrophobic.
We were pulling away from King's Cross train station and there was a loud bang in the tunnel.
The train just stopped and then all of a sudden it just filled with gassy smoke.
You couldn't breathe and it was stinging our eyes.
The lights went out and it just took a while for people to get to us.
It was very scary, we thought we weren't going to get out because we couldn't get off the train.
I was lucky. I was in one of the last carriages of the train.
There were guys trying to break the windows and they cut their hands.
There was a very loud bang.
The train derailed and there was smoke everywhere.
There was no fire but the smoke was very oppressive.
There were a lot of serious injuries down there as well - a lot of serious head injuries.
We waited for assistance from London underground and we managed to walk along the tracks back to King's Cross.
You couldn't see your nose in front of your face the smoke was so intense
We were stuck down there for about 20 to 25 minutes.
We managed to get outside the train quite quickly.
On the track it was a lot clearer. In the train itself, you couldn't see past your nose, the smoke was so intense. But on the track it was ok.
A lot of people had banged their heads against both the sides of the tube and into each other and a lot of glass was thrown everywhere which caused a lot of head injuries.
We were led to the main King's Cross station and we were seen to by paramedics and given water and oxygen.
As we left King's Cross, about 0855, there was an almighty bang and everything went totally black.
I started to shake with the relief of being alive
Then clouds of choking smoke filled the tube carriage and I thought I had been blinded. It was so dark that nobody could see anything.
I thought I was about to die, or was dead.
Then I realised I was choking, the smoke was like being underwater.
But gradually I could see, a little, as the emergency lights in the tunnel kicked in.
The glass was smashed so air started to flood in, we were OK.
There was silence for 10 seconds. Then a terrible screaming.
We all tried not to panic, saying to each other, "OK, stay cool, stand up if you aren't injured, hold hands, don't cry, stand up, hold on, we'll get out, the driver is trying to talk to us."
Some people screamed, some groaned, but we kept saying: "Shh, we'll get out, stay cool, the driver is talking to us, let's listen to him."
The driver said: "I've got to go forward a bit, then I can let you out, but first I need to make sure the track isn't live."
We all shouted the message into the darkness. It got passed down the train.
I was on the tube at Kings Cross when it was evacuated; the sight of the injured, blackened with soot, dirt and covered with blood is a vision that will stay with me for a long time.
I had to get away from the scene so I walked towards Euston only to be told that there had been another explosion, this time on a bus.
It seemed like confusion was at every corner.
Just after King's Cross there was a 'bang' coming from the front carriage.
The lights went out and emergency lighting came on.
Smoke came apparently from outside.
There were no announcement and some people started panicking after a while and tried to smash the doors, but only injured themselves.
After about 30 minutes two policemen opened the back door and let people out. I wonder why it took so long?
The smoke settled down after a while and I assume it was only dust spread around by the sudden Tube break.
We were only maybe 100m [328 feet] away from the platform but when you're inside you don't realise that.
I guess no-one was seriously injured on that train but I didn't see what happened to the people at the front carriage.
They should have passed information through though as the atmosphere in a packed Tube carriage is already frightening enough.
I would like to express my extreme gratitude to the London Underground staff, Fire Brigade, ambulance and hospital staff for their magnificent care and support for the passengers of the Piccadilly train disaster.
I was on that King's Cross train and for a moment I thought my number was up.
However, I was extremely fortunate to only suffer minor breathing difficulties due to the smoke and soot inhalation.
The after care at the Royal London Hospital was fantastic. Also a big thumbs up to the British public, people came together to help their fellow man and that really touched me.
My thoughts are with the families who have lost loved ones and those who were injured in all the incidents in London.