By Claire Heald
BBC News at King's Cross
The rumbling of trains can be felt underfoot as they travel deep in the tunnels around King's Cross station.
The number of floral tributes is multiplying
Up on the concourse, there are the footsteps of the crowd as Londoners persevere with their commute.
Suburban train services deliver people to the station on the city centre's northern edge. They cannot take the Tube on from here and walk out onto the street.
King's Cross remains a busy hub just a day after a bomb ripped open a tube carriage in a tunnel 100m beyond the station.
But the make-up of the crowd is different from usual.
Police man barricades at the street-level tube exits. Sniffer dogs are on patrol, rail staff bear information.
Firefighters ascend the stairs from the bomb site. There are volunteer religious ministers on hand. Reporters pose questions in a myriad of international accents.
Inside the train station, passenger queues snake around the concourse. They continue Thursday's interrupted journeys.
Survivors have returned to tell their story, demonstrate defiant normality and brave the Tube.
And on a wire fence by the sealed-off Tube stairs, people begin to leave flowers.
Underground, the Piccadilly Line is at a standstill as emergency crews recover bodies and anti-terrorist branch officers search for clues.
That means working conditions for firefighters and police are at 80-90 degrees Fahrenheit in a poorly-ventilated tunnel, says Euston firefighter Arrol Thomas.
"The situation will be very tough," he says. "I can't say what it's like or explain it, but it's carnage.
"It's harder afterwards - when you are dealing with it you just get on with it. But when you have time to reflect it's more difficult."
The area remains "very much a crime scene" for Chief Superintendent Willie McCafferty of the British Transport Police.
After the recovery and forensic examination, the next stage will assess the tunnel for safety before trains can restart.
On bomb train
The bomb that stopped them was at the end of Mark Margolis' carriage, or maybe in the next one.
He is not sure what happened before he heard a huge "clanging bang", the tunnel went dark, glass flew everywhere and the screaming began.
He feared fire most: "If there was a fire I didn't know how we would have got out of there."
Mark Margolis is determined to get back on the Tube
But he checked his injuries and clambered out along the tunnel, to the exit at Russell Square. There he joined the thousands of Londoners who called or texted loved ones to confirm they were safe.
"I started off by saying I am absolutely fine, which of course made her (wife Sarah) more worried because you never start a conversation with 'I am absolutely fine'."
He is back at the station to confront travelling on the Tube again.
That steely attitude is shared by Paul Dadge. He is here to do an interview on how he spent Thursday morning using basic first aid skills to treat victims in a shop's makeshift casualty area.
He cared for five or six of the more than 100 victims that were brought in to a store on the Edgware Road.
He says he has a "really useful message" for the bombers: "You won't affect us here in London.
'We'll be back'
"Most offices have told people to stay at home today, but once those Tube lines have been cleared we will be back in our offices."
He is mobbed by reporters from the UK, Europe, Asia, North America, India. Emergency vehicles wail past.
Outside the station, Joe Millard, 20, has come to lay flowers. There is now a row of tributes, poked in the fence, laid on the pavement.
He cancelled his journey home from Wolverhampton to Dover yesterday.
"I come through this station a lot. I just wanted to leave flowers here to express my sadness," he says.
Volunteer ministers are here, as is a chaplain for the police.
It is Rev Liam Johnston's job to make sure the incident's horror does not overwhelm officers in the tunnel or at the barricades.
"It is a scene down there of total carnage," he says. "They have to block that out and just treat it as a job until they come above ground.
Posters are appearing from worried friends and relatives
"I was talking to someone who questioned where God was in all of this? I said God was on that train, on that bus, he's here with us as we talk. They've been there, they understood."
"God bless your souls," reads the tribute on one of the bunches of flowers, which now number dozens.
"You think you'll defeat us. Let me take you by the hand and lead you through the streets of London, I'll show you something that'll make you change your mind," says another.
Therese Bjorn, 30, has come to add her tribute for the 21 people who died at King's Cross.
"There is nothing I can do but show my solidarity," she says.
"It could have been any of us. It's so indiscriminate."