BOSTON (REUTERS) - At Boston Children's Hospital, the list of the wounded included a 2-year-old boy with a head injury, a 9-year-old girl with leg trauma and six other children under the age of 15.

Over at Massachusetts General Hospital which was caring for 29 victims, injuries ranged from cuts and bruises to serious shrapnel wounds. Trauma surgeons said they had performed several amputations by mid-evening on Monday.

In total, three people lost their lives and more than 100 were injured when two bombs ripped through the crowd on a resplendent Monday afternoon at the finish line of the Boston Marathon, creating a gruesome scene of panic and carnage.

The explosions, which authorities said were 45 to 90 metres apart, knocked runners at one of the nation's most storied long-distance races off their feet and sent dozens of gravely injured spectators to the city's emergency rooms.

Images showed blood spattered along the street.

"It's really too easy to say how everyone is going to do," said Dr Peter Fagenholz, a trauma surgeon at Massachusetts General, who personally operated on six patients, none of them runners.

Boston Children's Hospital did not provide additional details about the children in its care. Most of the victims, who were sent to hospitals across Boston, have not yet been publicly identified by name.

Many runners were heading for the finish when a fireball and smoke rose from behind cheering spectators and a row of flags representing the countries of participants, video from the scene showed. The cheers turned to screams and panic.

Dr Fagenholz said the most serious cases - none of them children - arrived at the hospital within the first 15 minutes.

And while he said the injuries were not "other worldly," the scale of the incident caught him off guard.

He said the oldest patient he cared for was 71 years old.

"We take care of accidents all the time. It's just depressing that this was intentional," he said.

Dr Fagenholz said many of the patients would have a difficult recovery.

"A number of patients will require repeat operation tomorrow and serial operations over the next couple of days," he said.

"People, they are pretty brave, you know. It's a terrible thing and most patients attitude is, do what you need to do and try to make me better."