Concert-goer Abby Mullen decided to leave the Ariana Grande concert seconds before the last song finished so as to make it easier to get a taxi.
"As we were leaving a bomb or explosion went off centimetres in front of me," said Ms Mullen in a post on Facebook.
While she was "fine" and now back in her hotel, she said that human skin, blood and faeces "were everywhere including in my hair and on my bag".
She added: "We are being told it was a balloon/sound system but I can assure you it was not."
Police said 22 people, including children, were killed in the explosion at the concert in the northern English city of Manchester on Monday (May 23).
The first unconfirmed reports of an explosion emerged shortly after 2133 GMT (5.33am Singapore time).
Another 59 people were injured in the attack.
Another eyewitness Jade Baynes, 18, said armed police told her to run from the area after leaving the concert arena. She said she heard loud bangs and what sounded like gunshots just after the entertainment had ended, The Guardian reported.
Said Ms Baynes: "There were just a loud bang and a flash and everyone tried to scramble out. An alarm came on telling everyone to stay calm but leave as quickly as possible."
Mr Majid Khan, 22, was also at the concert when the incident happened.
"I and my sister, along with a lot of others were seeing Ariana Grande perform at Manchester Arena, and we were all exiting the venue when around 10.40-10,45pm-ish a huge bomb-like bang went off that hugely panicked everyone and we were all trying to flee the arena," The Guardian quoted him as saying.
"It was one bang and essentially everyone from the other side of the arena where the bang was heard from suddenly came running towards us as they were trying to exit Trinity Way and that was blocked so everyone was just running to any exit they could find as quickly as they could.
"Everyone was in a huge state of panic, calling each other as some had gone to the toilet whilst this had gone off, so it was just extremely disturbing for everyone there."https://twitter.com/elliefreyax/status/866830824561414145
A barman at the nearby Steven Charles Snooker Club, who wished only to be known as Tyler, told Britain's Press Association that he saw people lying on the ground covered in blood.
"We’ve had a few people in with panic attacks and in all kinds of disarray. We’ve got four girls here - trying to get them sorted to get picked up. There was a gentleman on the floor with his leg all bleeding and woman with blood down one side of her face. We felt something but didn’t know what it was - there was a sound like thunder. One girl had a panic attack and another had streaming tears, a woman had a heart attack just outside," he said.
Elena Semino, from Lancaster, was with her husband waiting for her daughter by the arena’s ticket office when the explosion went off, The Guardian reported. While she had a wound on her neck and a bleeding leg, she had not yet been seen by a doctor as her priority was finding her daughter – which she did.
Said Ms Semino: “My husband and I were standing against the wall, luckily, and all of a sudden there was this thing. I can’t even describe it. There was this heat on my neck and when I looked up there were bodies everywhere.”
Ms Semino's husband stayed behind to help an injured woman and has a minor injury. She ran to find her daughter in the auditorium. Her 17-year-old daughter Natalie and her friends said the performance had just come to an end when the explosion went off.
“It went off and then there was a moment’s silence and then there were screams,” said Megan Ryder, 19. They say security guards initially tried to calm them down, saying it was a popped balloon or a technical difficulty.
Said British Transport Police: "Officers are at Manchester Arena following reports of an explosion within the foyer area of the stadium at 10.30pm this evening.
"Emergency services are at the scene and we are working to establish more information regarding the explosion and will provide further updates as soon as possible."