Story highlights At least 144 people taken to hospital with wounds sustained from blasts

Doctors carry out amputations, reportedly pull ball bearings from victims

Three dead so far, including an 8-year-old boy

The full horror of Monday's bomb attacks in Boston was reflected in emergency rooms across the city as doctors were forced to perform amputations and treat injuries normally expected on a battlefield.

Around 11 p.m. ET, at least 144 people were reported to have been taken to hospital with wounds sustained from the blasts that brought terror and chaos to the city's annual marathon race.

Three people, including an eight-year-old boy, were killed, while at least 17 people are reported to be in a critical condition.

Designed to propel shrapnel

Images in the immediate aftermath showed people being carried away on stretchers -- one man in a wheelchair had blood all over his face and legs.

Photos: Deadly attack at Boston Marathon Photos: Deadly attack at Boston Marathon An injured man is loaded into an ambulance after two bombs went off near the finish line of the Boston Marathon on April 15, 2013. Three people were killed and at least 264 were injured. Hide Caption 1 of 55 Photos: Deadly attack at Boston Marathon A man comforts a victim on the sidewalk at the scene of the first explosion. Hide Caption 2 of 55 Photos: Deadly attack at Boston Marathon The second explosion goes off near the finish line. Hide Caption 3 of 55 Photos: Deadly attack at Boston Marathon The first explosion knocked down 78-year-old runner Bill Iffrig at the finish line. He got up a few minutes later and finished the race. Hide Caption 4 of 55 Photos: Deadly attack at Boston Marathon A runner embraces another woman on the marathon route near Kenmore Square. Hide Caption 5 of 55 Photos: Deadly attack at Boston Marathon Former New England Patriots offensive lineman Joe Andruzzi carries a woman from the scene. Hide Caption 6 of 55 Photos: Deadly attack at Boston Marathon A victim of the first explosion is helped on the sidewalk of Boylston Street. Hide Caption 7 of 55 Photos: Deadly attack at Boston Marathon An injured person is taken away from the scene in a wheelchair. Hide Caption 8 of 55 Photos: Deadly attack at Boston Marathon A woman kneels and prays at near the finish line. Hide Caption 9 of 55 Photos: Deadly attack at Boston Marathon People run down Exeter Street after the blasts. Hide Caption 10 of 55 Photos: Deadly attack at Boston Marathon The explosions occurred around 2:45 p.m., about an hour after the first of the race's nearly 27,000 runners had crossed the finish line. Hide Caption 11 of 55 Photos: Deadly attack at Boston Marathon Victims lie on the ground at the scene of the first explosion. Hide Caption 12 of 55 Photos: Deadly attack at Boston Marathon A couple runs from the scene pushing a stroller. Hide Caption 13 of 55 Photos: Deadly attack at Boston Marathon A runner reacts near Kenmore Square after the explosions. Hide Caption 14 of 55 Photos: Deadly attack at Boston Marathon A man's blood-stained feet hang outside an ambulance. Hide Caption 15 of 55 Photos: Deadly attack at Boston Marathon A bystander who was injured in the first explosion is wheeled across the finish line while receiving medical attention from rescue workers. Hide Caption 16 of 55 Photos: Deadly attack at Boston Marathon Carlos Arredondo was at the race handing out American flags to spectators. After the blasts, he helped emergency responders and is credited with helping a man survive serious leg wounds. Hide Caption 17 of 55 Photos: Deadly attack at Boston Marathon The second explosion goes off near the finish line. Hide Caption 18 of 55 Photos: Deadly attack at Boston Marathon Police look at blown-out windows. The bombs shook buildings, witnesses said, sending people to seek shelter under tables. Hide Caption 19 of 55 Photos: Deadly attack at Boston Marathon Unclaimed runners' bags fill an area near the marathon finish. Hide Caption 20 of 55 Photos: Deadly attack at Boston Marathon Women desperate to hear from loved ones are unable to get close to the site of the attack. Hide Caption 21 of 55 Photos: Deadly attack at Boston Marathon Police and runners stand near Kenmore Square after the attack. Hide Caption 22 of 55 Photos: Deadly attack at Boston Marathon Runners gather near Kenmore Square after the explosions. Hide Caption 23 of 55 Photos: Deadly attack at Boston Marathon An EMT worker is transferred to an ambulance outside a medical tent in Copley Square. Hide Caption 24 of 55 Photos: Deadly attack at Boston Marathon A SWAT team arrives on the scene. Hide Caption 25 of 55 Photos: Deadly attack at Boston Marathon A runner sits near Kenmore Square after the attack. Hide Caption 26 of 55 Photos: Deadly attack at Boston Marathon Runners who had not yet finished the race are stopped after the explosions. Hide Caption 27 of 55 Photos: Deadly attack at Boston Marathon Victims are helped at the scene of the first explosion. Hide Caption 28 of 55 Photos: Deadly attack at Boston Marathon A man in tears is helped at the scene on Boylston Street. Hide Caption 29 of 55 Photos: Deadly attack at Boston Marathon Passersby put pressure on a victim's leg to try to stop the bleeding. Hide Caption 30 of 55 Photos: Deadly attack at Boston Marathon Massachusetts State Police guard an area near Kenmore Square. Hide Caption 31 of 55 Photos: Deadly attack at Boston Marathon Bystanders embrace near the finish line. Hide Caption 32 of 55 Photos: Deadly attack at Boston Marathon Police officers gather on Newbury Street. Hide Caption 33 of 55 Photos: Deadly attack at Boston Marathon Women and children are escorted away from the scene. Hide Caption 34 of 55 Photos: Deadly attack at Boston Marathon Bomb squad officials check a possible suspicious device near the scene of the blasts. Hide Caption 35 of 55 Photos: Deadly attack at Boston Marathon A woman is comforted after the blasts. Hide Caption 36 of 55 Photos: Deadly attack at Boston Marathon Two injured women are taken away on stretchers. Hide Caption 37 of 55 Photos: Deadly attack at Boston Marathon An injured woman is loaded into an ambulance. Hide Caption 38 of 55 Photos: Deadly attack at Boston Marathon First responders load injured people into an ambulance. Hide Caption 39 of 55 Photos: Deadly attack at Boston Marathon An injured man is prepared to be moved from a stretcher to an ambulance. Hide Caption 40 of 55 Photos: Deadly attack at Boston Marathon An injured woman is placed on a stretcher. Hide Caption 41 of 55 Photos: Deadly attack at Boston Marathon A runner is comforted following the attack. Hide Caption 42 of 55 Photos: Deadly attack at Boston Marathon The Cambridge Police Department's bomb squad investigates unattended personal items left behind after the explosions. Hide Caption 43 of 55 Photos: Deadly attack at Boston Marathon Bystanders check their mobile devices for news of the explosions. Hide Caption 44 of 55 Photos: Deadly attack at Boston Marathon A member of the bomb squad investigates a suspicious item on the road near Kenmore Square. Hide Caption 45 of 55 Photos: Deadly attack at Boston Marathon A runner in a wheelchair is taken from a triage tent after the explosions went off. Hide Caption 46 of 55 Photos: Deadly attack at Boston Marathon People comfort each near the site of the blasts. Hide Caption 47 of 55 Photos: Deadly attack at Boston Marathon Racers and race officials stand by after the explosions. Hide Caption 48 of 55 Photos: Deadly attack at Boston Marathon Emergency personnel respond to the scene. Hide Caption 49 of 55 Photos: Deadly attack at Boston Marathon Police and emergency crews tend to victims. Hide Caption 50 of 55 Photos: Deadly attack at Boston Marathon An injured woman is carried away on a stretcher. Hide Caption 51 of 55 Photos: Deadly attack at Boston Marathon A man lies on the ground after the incident. Hide Caption 52 of 55 Photos: Deadly attack at Boston Marathon Officials watch as the first explosion goes off on Boylston Street. Hide Caption 53 of 55 Photos: Deadly attack at Boston Marathon Spectators leave the bleachers after the explosions. Hide Caption 54 of 55 Photos: Deadly attack at Boston Marathon Police inspect one of the blast sites. Hide Caption 55 of 55

JUST WATCHED Runner: Shock waves hit my whole body Replay More Videos ... MUST WATCH Runner: Shock waves hit my whole body 04:14

JUST WATCHED Producer captures Boston blast on video Replay More Videos ... MUST WATCH Producer captures Boston blast on video 02:29

JUST WATCHED Runner: Bombs sounded like Afghanistan Replay More Videos ... MUST WATCH Runner: Bombs sounded like Afghanistan 02:25

While many patients were treated for cuts and scrapes, doctors have also been "pulling ball bearings out of people in the emergency room," suggesting the bombs were designed to propel shrapnel, according to one terrorism expert briefed on the Boston blasts, though CNN is yet to confirm this.

Medical teams have also carried out at least 10 amputations and treated many leg injuries, suggesting the device was low to the ground, according to CNN's Deborah Feyerick.

Among the 28 people taken to the city's Brigham and Women's Hospital, the most common types of injuries are to the bone and tissue, hospital spokesman Tom Langford told CNN.

He said nine of those patients have potentially limb-threatening wounds. A 3-year-old victim was transferred to Boston Children's Hospital for treatment.

Amputated limbs

Dr. Peter Fagenholz, a trauma surgeon at Massachusetts General Hospital, told reporters he treated many of the 29 patients who arrived at the hospital for shrapnel wounds.

"Many of the victims were hit with "a lot of small, metal debris," he said.

"Some people have asked already whether they were BBs or parts of bombs," he said, referring to earlier reports that ball bearings have been pulled from victims. "We can't say whether they were placed their intentionally or whether they were just part of the environment."

He said the most serious wounds "have been combined, complex lower injuries that involve blood vessels, bone and tissue." Some of the patients had to have limbs amputated, Fagenholz added.

"A number of patients will require repeat operations and serial operations over the next couple of days," he said, adding that he had been in surgery for almost 14 hours.

Describing the horror

Theresa Panter, who had been running in the marathon, described the scene as she approached the finishing line.

"When I heard the bomb and saw the reaction of the spectators, I was just alarmed. Then I was pushed back by a spectator and then a Boston Athletic official -- he grabbed a bunch of us and pushed us back. It was pretty upsetting."

Her husband, Dr. Allan Panter, was in the crowd and described how he ended up tending to people on the streets.

"I saw at least six to seven people down next to me -- they protected me from the blast. One lady expired, one gentleman lost both his limbs, his lower extremities. Most of the injuries were mainly lower extremity injuries.

"I could not figure out why the young lady had expired, I could not find any injury on her thorax."