Here is a selection of eyewitness accounts we received from people involved in the explosion at Liverpool Street.
We just pulled out of Edgware Road and the next thing I knew there was a large flash of light.
There was a burning sensation on my hands - I put my hands up to my face.
I was on the floor by that point.
As soon as I realised there'd been an accident I got up, had a look around, and saw where the exits were.
The train was at a complete standstill.
The lights were out and there was a lot of smoke in the carriage.
On the tube there was, I would say, maybe six or seven people lying on the floor.
A lot of people with a lot of blood on their faces and ripped clothes.
I was in the eastbound Circle line train just coming into Edgware Road when the westbound train in front of us exploded.
We felt a sudden bang, all the lights went out and the carriage filled with dust.
People were very calm, despite screams from the westbound train now opposite us.
We didn't take the incident too seriously - despite the smoke and the screams - until we saw people covered in blood in the other train.
When we were taken off we could see debris from the other train just in front of ours.
Our train got away with broken windows and doors as far as I'm aware.
What else can I say? Not a fun experience.
I was on one of the trains involved, not the one with the bomb but the one passing it in the tunnel coming from Paddington.
There was a flash and a bang and we were thrown across the carriage. We all thought it was a crash and that we had hit the oncoming train.
I didn't learn that it was a bomb until much later. All the lights went out and there was dust and soot everywhere, which I got covered in.
I could hear a man crying out: "Please help me". Various passengers tried to open the carriage doors by force unsuccessfully.
We were in the front carriage and the driver came through to let us know help was on the way.
This ticket was purchased at Edgware Road just before the blast
He told us that they were clearing debris from the track in front of us.
Everyone was quite calm. After a few minutes more London Underground (LU) staff arrived.
They put a ladder down from the front of the train and led us out.
We had to pick our way over the debris.
I could see the remains of bits of a tube carriage including bits of the carriage wall where you could see the stuffing poking out.
LU staff lined the way as we walked towards Edgware Road station and up onto the platform.
I saw some people with minor cuts and bruises but nothing major.
I count myself very lucky to have survived as I was yards away from the blast.
I was in carriage one on the Edgware Road train and I am physically OK.
I bought a ticket at Edgware Road at 0843 and was on the train after five to six minutes.
Thirty seconds after leaving the station there was a blast.
London Underground Staff were wonderful and had to deal with everything for 30 minutes before any paramedics arrived.
Staff in Marks and Spencer and at the Hilton hotel were just wonderful. They were looking after everyone.
I was on the Circle Line train to Edgware Road this morning - the same train that blew up moments after I disembarked.
As I made my way along the platform I saw the rear of the train (westbound) entering the tunnel followed by a loud explosion.
It was almost 30 to 40 minutes before the police or emergency services reached the scene, but as they arrived they dealt with the casualties and secured the area with great calm and professionalism.
A friend of mine who was still on the train continuing his journey to work was one carriage in front of where the blast occurred.
I was glad to see him come out around an hour later without any serious injuries, though he told me of people that were far worse off.
Most people were shocked and in a trance about the whole incident.
Passengers that were being evacuated from the trains below were taken into the nearby Marks and Spencer for basic first aid and water.
Police on the scene assisted with any help that was needed.
I was in the train when the blast occurred between Edgware Road and Paddington.
I heard the immense bang and tried to look out the window.
All I saw was another train passing by mine and the two were stopped very close to each other in the tunnel.
Right after the explosion, thick black smoke came into our carriage.
It was powdery, thick smoke. Everyone tried to cover their noses and mouths with handkerchiefs and tissue paper.
I am still in shock, but I appreciate that I am still alive and unhurt
It seemed to last a long time, but it must have been less than two minutes until we were told to evacuate the train.
I was in the second carriage so I had to go through the first one in order to evacuate.
When I reached the end of the first carriage, I thought I would see the driver's compartment, but it was totally blown off.
I saw parts of the compartment - such as the doors and the roof - scattered around the track.
I was helped down to the track by underground staff and we walked all the way to the Edgware Road station in the dark tunnel.
I cannot tell you how happy I was to see the sky and have non-coloured air when I reached ground level.
I walked home in the rain. I am still in shock, but I appreciate that I am still alive and unhurt.